Depending on location ... different Basilicas , cathedrals , or churches have their own rules

I noticed while reading guidebooks some churches require payment to see certain rooms,. but not the entire building. Could that be it or are you referring to churches that charge people to enter?

yes, churches that charge to enter. To me it seems there is a country called Italy, but it really is a composite of regions that have their own customs and rules. Similar to Brittany and Provence in France or NY and Miami in the USA ...same country, totally different culture.

It was my impression during a lengthy trip to Italy last year that, aside from select parts of churches like treasuries and crypts which often do have separate admission procedures, when I was asked to pay to enter a church, it was no longer being used for religious services. It wouldn't be reasonable to expect people to pay to attend services or go to confession.

To me the cost is nominal especially when you think of the increased amount of work for cleaning and staffing that must go in to having increased traffic thru their holy space. I have paid to enter Orvieto and Siena for the whole church, not just a Treasure Room or crypt or special display.

It has also been my experience in UK that if you go for a service there is no charge. I'm thinking about Westminster Abbey, Salisbury Cathedral and Bath Abbey all of whom have a charge or ask for a donation for visiting but allow you in for church functions.

I have no problem at all paying to enter a historic site whether it is a church or a ruin. The money to maintain it has to come from somewhere. It sure won't be the Italian government. They are broke.

I think you will find a wide mix. Yes, many churches have no admission, many do have areas, a Treasury or to climb the bell tower, that they charge admission, others have limited times and areas for worship at no charge, with a hefty admission at other times, others a suggested donation. Italy is not a special case, I ran into a variety in Spain, London has both Westminster and St Pauls that charge a more than nominal fee to enter. So in a way that is just the way it goes just about anywhere.

I read some churches have a policy not to enter during services just to look around, but I'm not sure you would get kicked out for that. Regardless, it is inappropriate to do that during mass.

A working church will not charge admission to the worship space, but may charge for various special rooms or areas. A decommissioned church which functions as a museum may charge admission. Chapels, which are not parochial, can charge admission.

It doesn't depend on location, but on function.

I noticed on our RS Italy tour that we were often give admission into a church. Unfortunately, it seemed that what we really wanted to see required an additional charge.

A working church will not charge admission to the worship space, but may charge for various special rooms or areas.

I could be wrong, but I believe most of the churches covered by the Chorus Pass in Venice are "working churches", and one must pay to enter any portion of these buildings--the cashier is right inside the door. And, like others, I have no problem paying for the privilege to see them and to help in some small way with the upkeep.

The policies vary even within a city. In Florence entry to the main area of the Duomo is free. On the other hand you have to pay in to Santa Croce. Both are working churches. You never pay entry if you are attending a service.

Similarly in London, you pay in to both Westminster Abbey and St Paul's Cathedral, which are also working churches, but not for a service. All the other churches in London are free.

Most churches are owned by the Italian state, that pays for most of the maintenance, with possible access fees making for the difference. There may be specific bodies administering maintenance - in Florence, for example, the Cathedral, St. Lorenzo and St. Croce have each a foundation with mixed representatives from state and church taking care of the maintenance. St. Peters in Rome is not in Italy - it is in the Vatican and directly administered. Unbeknown to most, also St. Francis in Assisi and St. Antonio in Padova are considered as Vatican territory and have the same extraterritorial status of foreign embassies. You understand that there are many possible situations and a common policy is not possible.

Fees do seem to be based on a mix of function and administration versus region. The sanctuaries themselves may be free but a satellite structure (bell tower, baptistry, museum, etc.) crypt or Roman excavation underneath involved an entry fee. I'd also paid a photography fee for the duomo in Milan - which has evolved into a general entry ticket since last we were there.

Westminster in London was the highest ticket I've paid for a church so far - done it twice and will do it again - and I see that St. Paul's has gone up quite a lot since the last visit. In Belgium, most of the churches were free but a few had fees for specific pieces of art - "Adoration of the Mystic Lamb" at St. Bavo's comes to mind - or art collections. Photography fee for the cathedral in Aachen; fee for crypts in Munich; towers and crypt at Notre Dame, Paris; etc.

My experience has been that even "working churches" might charge admission unless there is a mass about to start. A lot of churches that charge for tourist entrance do shoo the tourists out before the mass is to start. If you're there to attend a mass, there's often a special entrance for that.

Oh, and you often have to pay to turn on the lights for specific items of interest. It's on a timer.

Active churches do not charge to attend services but they often charge tourists using them as art museums. For example in Orvieto there is a special gate to enter for mass that is no charge but doesn't authorize you to wander about taking pictures throughout the Cathedral. I have seen similar at other working churches where mass is regularly held. The same was true in Spain. Even the Mezquita allows free entry for mass.

I have no problem at all paying to enter a historic site whether it is a church or a ruin. The money to maintain it has to come from somewhere. It sure won't be the Italian government. They are broke.

I don't undestand if you're trying to be funny or you really believe what you wrote, but in 2016 the national government allocated 180 millions of euro only for special restoration projects.
The Ministery for Cultural Heritage manages a 2 billions euro budget of taxpayers' money for routine maintanence, studies, salaries, excavations and exhibitions.
Plus EU funds.

Plus the money given by Regions and Cities. Plus the deductible donations made by corporations, banks and italian citizens.

Last, and least, tickets and fees paid by tourists like you.

As 2 billions euro is less than 0.5 % of the total national budget I wouldn't say we're broken, not yet.

Most churches are owned by the Italian state

Most churches are owned by the office of the local bishop and get money from the Italian state. Other are owned by Religious orders and get money from the Italian state.

A few are part of the Vatican State and get money from the Italian state and also from Italian citizens who can donate a small part of their taxes to their favorite religion. To be fair the Catholic Church agrees not to use this money for clergy, but only for the maintenance of churches and hospitals or for Charitable projects.

I don't know any active church that's owned by the state, but if I had to guess I'd say Santa Croce in Florence and the Pantheon in Rome.

When Italy was unified under Piedmont rule in 1861, the Piedmont laws were extended to whole Italy and in 1866 most church properties, mostly monasteries and adjoining churches, were assigned to the state. - This is why, by the way, so many Italian barracks, hospitals, schools, academies and public offices are hosted in former monasteries. For example, as you get out of your train at Florence SMN, the huge building between the station and the church was the church monastery and now houses a Carabinieri undergraduates school. - So, while churches built after 1866 are likely ownership of Catholic church, you cannot be sure about older ones; if they are by a monastery, no matter if the monastery is no more working, they are likely to be owned by the state. S. Lorenzo, S. Marco, S. Croce, S. Miniato, S. Spirito, S. Maria Novella are all examples in Florence.

A working church will not charge admission to the worship space, but may charge for various special rooms or areas. A decommissioned church which functions as a museum may charge admission. Chapels, which are not parochial, can charge admission.
It doesn't depend on location, but on function.

This is not true. It varies by church, not function. The mix, as described by Jim, is quite true, in Italy and throughout Europe.

A church will never charge admission for regular services and often closes to the public during such services. Larger churches often have an area or chapel reserved for services while the public can come and go.

Remember that most churches in Italy are art galleries and the Italian government does not have the funds to maintain them and other historical places hence the fees to visit them as indicated in other posts,well worth the cost.
Mike