BOSTON (AP) -- Former Massachusetts House Speaker Salvatore DiMasi has asked the U.S. Supreme Court to reverse his conviction on public corruption charges and grant him a new trial.

There is no guarantee the country's highest court will consider DiMasi's petition filed last week, said his lawyer, Thomas Kiley.

"Very few petitions for cert are granted," Kiley told the Boston Herald (http://bit.ly/1hyR0K0). "It's the last direct appeal you have."

Federal prosecutors have until Jan. 21 to file their response. A spokeswoman for U.S. Attorney Carmen Ortiz declined to comment.

DiMasi, a Democrat, was convicted in 2011 of conspiracy, extortion and theft of honest services by fraud, a bribery charge. He was accused of using his political clout to steer lucrative state contracts to Cognos, a Canadian software firm with U.S. headquarters in Burlington, in exchange for payments of $65,000.

A federal appeals court upheld the conviction in August.

DiMasi, 68, who resigned in 2009, was the third consecutive Massachusetts speaker to leave office under a cloud of suspicion.

The Supreme Court petition says the $65,000 came from legitimate fees for referring his law partner to Cognos for contract work, and that attorney-client privilege protected him from disclosing the relationship to the state, Kiley said.

"Ours is a state-law thrust," Kiley said. "We are of the view that when you want to evaluate the intent of a state lawmaker, you must consider state law."

DiMasi is being treated in prison for advanced throat and tongue cancer.

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Information from: Boston Herald, http://www.bostonherald.com