The Cumbrians handed the 26-year-old permission to talk to U's boss Paul Lambert after he showed strong interest in the shot stopper.
Williams, who only arrived at Brunton Park from Crewe last summer, duly impressed in his debut season for the club, making 36 appearances.
Manager Greg Abbott told Carlisle's official website: "There has been an offer for Ben and he is now talking to Colchester to see if it is a move that he wants to make.
"It is a deal that does have a slight complication involved with it at the moment, but it's a complication that is in our favour. We should have more details about that later this week.
"Obviously if he does agree to go then we will move to bring in a replacement, and work is already being done on that. We would want that one sorted as quickly as possible, but we have to wait and see what happens with Ben and his talks with Colchester first."