Lawyers for Michael Avenatti on Monday asked a Manhattan federal judge to dismiss a criminal indictment accusing the embattled attorney of waging a multimillion-dollar extortion plot against athletic apparel company Nike Inc., saying their client had been acting in his legitimate capacity as an attorney.

The filing, in the U.S. District Court for the Southern District of New York, continued a multipronged attack from Avenatti’s Florida-based attorneys, Scott A. Srebnick and Jose M. Quinon, who last week accused federal prosecutors of carrying out a political witch hunt against their client.