PORTLAND, Maine — Federal prosecutors said the former manager of one of the state’s largest lobster cooperatives should get a prison sentence substantially more severe than his co-conspirator in a scheme to illegally sell the seafood.

The U.S. Attorney’s Office filed its recommendation Tuesday in U.S. District Court in Portland in their case against Robert Thompson of St. George. Thompson was the longtime manager of the Spruce Head Fishermen’s Cooperative.

Thompson pleaded guilty in December to one count of tax evasion and one count of violation of the Lacey Act, which prohibits the illegal sale of lobsters. Defense attorney Walter McKee has requested a sentence of 45 days, which is what John Price of J.P. Seafood of Eliot received as part of a clandestine arrangement with certain members of the cooperative to buy lobsters from them in cash.

But U.S. Attorney Thomas Delahanty said Thompson’s actions warrant a sentence substantially more severe than 45 days. Price reported the income he made while Thompson did not, leading to the tax evasion charge.

The state’s chief prosecutor also said Thompson deceived and misled the members of the Spruce Head Fishermen’s Cooperative, who employed him, paid him well and entrusted him with significant authority and discretion in the conduct of that business.

Thompson’s scheme created a situation where not only he but other complicit cooperative members were receiving significant cash payments off the books that were virtually impossible for taxing authorities to detect, the federal prosecutors stated in their sentencing recommendation.

Thompson originally was charged with felony theft of lobsters, but that charge was dropped after federal investigators learned several cooperative members were selling their lobsters through Thompson to Price for cash.

The prosecutors argue Thompson evaded $114,000 in federal income taxes from 2004 through 2011.

Thompson is scheduled to be sentenced Thursday.