Well, not quite the "Spanish help" you asked --things and laws are not always exactly the same here in Catalonia and you're referring to a train service elswhere in Spain-- but in principle, you should know that strikes in services deemed "of public interest", such as train transportation or emergency services, for example, are never "full strikes" -that'd be illegal. When a strike in such services is called, the appropriate authority (the government of the autonomous community affected or the national government... depending on different variables of no concern here and now) declares a "minimum level of service" (servicios mínimos) that has to be offered so as not to collapse the region/country or as to endanger the population beyond reasonable parameters (ie emergency services) while preserving, at the same time, the workers' right to strike -which is enshrined in the Spanish Constitution.
Thus, in train transportation, this normally translates to a % of trains of that day that have to be working and at certain time bands. So, for example, this might turn in that there'll be 50% of the normal trains during rush hours from 6-9am and from 7-9pm, and 33% for the rest of the day (that's 1 in 3 working). There can be different %s for commuting and for long distance trains. Commuter trains always have a minimum service, long distance trains "almost" always.
These %s are established on a case by case basis, that is, for every strike and only after the unions have officially convoked the strike -which is done by the unions presenting a form to the Gov Registry indicating the reasons for the strike and the dates proposed. Then, the proper authority defines which should the "servicios mínimos" be for each of the proposed dates.
So far, as far as I know, the unions have not yet "formalized" the strike... they've only announced the intention to do so. Therefore, until the strike is not "official", so to speak, there'll be no minimum service level announced. In principle, if we're talking about a strike at the end of this month, I would imagine that if it "has to be" then it'll be formalized within a few days or so (as each step of the process has its tempo). The only information available as of today only indicates that a 1-day strike is being "considered": https://economia.elpais.com/economia/2017/09/05/actualidad/1504613705_028880.html
Probably this isn't helping you much, but at least you know the background of striking here.
