Federal prosecutors want the judge overseeing the upcoming trial of notorious drug-cartel boss Joaquin “El Chapo” Guzman to question the kingpin’s new attorney — claiming the lawyer might have a conflict of interest.

Lawyer Jeffrey Lichtman, who officially joined Guzman’s defense team last month, “has represented three potential cooperating witnesses for the government,” the feds wrote in a new filing.

“Because of his prior representation of these government witnesses, he may not be able to ethically cross-examine these witnesses without their consent,” the court papers say.

The defense attorney challenged the government’s claims.

“I vehemently dispute the assertion that I represented three individuals who might be testifying against Mr. Guzman,” Lichtman told The Post.