The show's creator Ryan Murphy confirmed that the stars' characters will be written out of the show as they graduate at the end of the forthcoming third season.
He told The Hollywood Reporter that the decision was made in an effort to keep the show 'realistic'.
'You can keep them on the show for six years and people will criticise you for not being realistic, or you can be really true to life and say when they started the show they were very clearly sophomores and they should graduate at the end of their senior year,' he said.
And they won't be the only people to move on, said Murphy, adding that 'more characters are leaving than are staying' following graduation, although their identities won't be revealed until the time comes.
'We've never done anything by the book,' he said. 'We made that decision and I involved Chris and Lea and they thought that was a good idea. They both trust the writing and trust me and felt that it would be great to have an open and closed experience for them to go out while they were on top.'
But he admitted that he still hasn't discussed the plans with Monteith, who plays Finn in the musical series, although he thinks that he probably knows that his time is coming to an end. 'He knows he was a sophomore when the show started.'