Is an employer required to give an employee restroom breaks, when the privilege is being abused?

At my workplace there is an employee who takes the "average" restroom breaks that any one else does, but also takes 3-4 additional breaks a day that are an extended period. The employee will come into work at 8am, clock in and be in the restroom for 15-20 minutes. After our hour lunch (not paid) the employee will clock in, and head straight to the restroom for another 15-20 minutes. Usually at some point in the afternoon he will go in the restroom again for another 15-20 minutes. Keep in mind that in between these extended period restroom breaks he is using the restroom. What can we legally do? Can we make him clock out, or do something to limit the breaks? I wouldn't be surprised if he uses close to an hour and a half of his 8 hour work day in the restroom.