Diddy is firing back at federal prosecutors who are opposed to throwing out his conviction on Mann Act charges in his criminal case … he says Uncle Sam is using the wrong definition of prostitution to prosecute him under the Mann Act, and says he deserves, at minimum, a new trial.

In new legal docs, obtained by TMZ, Diddy’s legal team take shots at the feds as they try to make the case for Judge Arun Subramanian to change Diddy’s Mann Act conviction to an acquittal or give him a new trial.

Diddy says prosecutors are using the modern definition of “prostitution” to apply the Mann Act, a federal law that was enacted way back in 1910 … when it was also known as the White Slave Traffic Act.

The defense says the court should grant an acquittal in Diddy’s case, or at least a new trial.

As you know … Diddy was acquitted July 2 of racketeering and sex trafficking charges, and a jury only found him guilty on two lesser charges of transporting people for the purposes of prostitution under the Mann Act.

We broke the story, Diddy filed a motion a couple weeks after the verdict came down … asking for an acquittal or a new trial. Prosecutors opposed it and now Diddy is firing back and doubling down.