It turns out that the actors found out that Jennifer Lawrence is making $10 million for the movie and they had only been offered chump change in comparison, approximately $2 million each. I can understand why Josh as Peeta would be upset because he was a central figure in the first movie as well.
'The Hunger Games' was a trilogy of books written by Suzanne Collins. The books are dystopian and amazing and the first movie did well in trying to accurately portray the book.
Perez Hilton reports that a movie insider states:
“Liam and Josh got wind of Jennifer’s significant pay raise and they want more money to appear in the second movie of the tetralogy. They’re not demanding as much as Jennifer, they’re aware she plays a bigger role in the films, but they want a little more than the $2 million they were each offered."
I think that isn't too much to ask seeing as the movie made millions and millions of dollars. I hope the studio doesn't get cheap and try to replace them. They are vital actors in the sequels.