From the previous reply it would seem that the strike is not a "done deal". Anybody have any thoughts on this?
Would the trains also be affected, or is this just a private company's labor issues? Does anyone know if another bus company goes to Salamanca?
It just affects Auto-Res, their workers, and their customers. They are negotiating a new colective agreement and things seem no to be too smooth. The series of consecutive strikes began in early March and during every Monday, Friday and Sunday of May Auto-Res will offer only what's called "servicios minimos" (that is, "minimum services") that possibly include only one daily service in each direction in all their routes. All this is subject to changes if they reach an agreement, of course.
RENFE is not affected at all by this strike, so your best bet is taking the train, as no other company serves the Madrid-Salamanca route. As far as I know, bus routes in Spain are concessions from the Government and are assigned only one company per route/area.