Don Imus (file photo)

Don Imus reportedly plans to sue CBS Radio in an attempt to collect the $40 million balance on his contract.

According to Fortune.com, the controversial radio host has hired New York attorney Martin Garbus, who specializes in handling cases involving free speech issues.

A source told Fortune.com that Imus' lawsuit highlights language in his contract which encouraged him to be confrontational and irreverent on the air. The contract also supposedly stipulates that Imus receive a warning prior to being fired.

CBS President Les Moonves fired the 66-year-old Imus on April 12, after he made racially insensitive remarks about the Rutgers University women's basketball team.