Lawyers for a former portfolio manager say prosecutors' recommendation that he serve up to 20 years in prison for insider trading is "outrageous" and "irrational."

Mathew Martoma's lawyers said in papers filed late Tuesday that a judge next month would have to conclude Martoma teamed up with his billionaire boss — Steven A. Cohen — to conclude he deserves such stiff punishment. The Probation Department recommended Martoma receive from 15.7 to 19.6 years in prison. The lawyers said the government never proved Martoma provided Cohen with inside information.

Cohen has not been criminally charged, but the Securities and Exchange Commission has accused him in a civil action of failing to prevent insider trading at his company, SAC Capital Advisors. He has disputed the allegations.

Martoma was convicted in February.