NEWARK, N.J. — On the eve of the George Washington Bridge lane-closing trial involving two former allies of Republican Gov. Chris Christie, the two sides are clashing over whether the government has changed its theory of the case.

An attorney for Bill Baroni wrote in a court filing this week that prosecutors now claim his motive was to curry favor with Christie by causing traffic jams to punish a mayor who didn’t endorse Christie’s 2013 re-election.

That allegation isn’t in the May 2015 indictment of Baroni and former Christie staffer Bridget Kelly, attorney Michael Baldassare wrote on behalf of Baroni. He argued prosecutors shouldn’t be able to present that motive to the jury.

The government “has never presented, proffered, or relied upon — and Mr. Baroni has not located — a single document in the over 1.7 million pages of discovery that in any way supports his prosecution on this allegation,” Baldassare wrote.

Baroni, a former top executive at the Port Authority of New York and New Jersey — the bridge’s operator — and former Christie staffer Bridget Kelly are charged with fraud, civil rights and conspiracy charges. Opening statements are scheduled for Monday in Newark.

The most serious charge carries a maximum prison sentence of 20 years.

Christie hasn’t been charged.

In a response filed Thursday that had several passages blacked out, prosecutors contended the question of motive matters less than the fact Baroni joined in the alleged scheme.

“Any motivation Baroni might have had for misusing Port Authority resources is sufficient, so long as the statutory elements are met,” they wrote.