Planning on a train operated by SWR which is the line towards Portsmouth (from Waterloo), Salisbury, Hampton Court, Surbiton, Basingstoke or pretty much anything else in that direction and everything out of Waterloo station?
In December?
Sorry, the same issue from the last several years drags on and the union has announced 27 days of strikes from 2nd of December through to New Year, stopping the strike only for one day for the General Election on the 12th of December and for two days over Christmas and Boxing Day when although there won't be a strike there are never any trains anyway.
You would do well if you will be impacted by the strike - and if travelling on SWR you will be - to consider alternate routes or methods of travel.
UPDATE: As of Friday evening November 29, 2019 this strike is going ahead. All services in and out of Waterloo station will be affected one way or another until next year. There have been several meetings between the union and the company but there is not a settlement. No more talks are expected. The strike will start on Monday. 900 or more services daily, nearly 25,000 over the course of the strike. These will be the worst consecutive walkouts in British railway history.
Further updates will be posted if there are changes.