1 Marvel actors can't act in DC movies when then are doing a Marvel movie, this is one of the most important and absolute restriction every actor should follow.
2 From 2015, marvel main lead in movies can't smoke and the reason is after Disney accusation of marvel. Disney made this rule to make make franchise family friendly.
3 All marvel actors doesn't sign for year long contracts, they make contract to number of films appearing, normally marvel make contracts for 6 films.
4 Background checks, this made many marvel actors and directors nervous because everyone who is in the marvel studios need to go through background check, simply James Gunn was fired because his tweets that he made long before he is part of Marvel, but he was rehired by Marvel now.
5 Marvel doesn't disclose their scripts until the day of shoot, unlike another studios where actors know all about the story.