Colchester have released Matt Briggs and Lloyd Doyley.
Left-back Briggs, who joined the U's permanently two years ago, was sidelined for the first half of this season following a hip operation, but made 15 appearances on his return.
Veteran defender Doyley signed for Colchester last October, but only played three first-team games.
All of the club's other out-of-contract players have been offered new deals.