Jones Day’s work for the City of Detroit during its bankruptcy earned the firm nearly $58 million in legal fees and high praise from the federal judge overseeing the Chapter 9 case. Now Jones Day’s work is being questioned—and the firm’s managing partner is fighting back.

Detroit Mayor Mike Duggan last month threatened to sue Jones Day after he said the firm and the emergency manager it represented, Kevyn Orr (who has since returned as a Jones Day partner), hid from the mayor’s office figures used to estimate the cost of the Motor City’s pension liability as part of a bankruptcy exit plan approved in 2014. That came after new estimates show that pension liabilities have grown by nearly $500 million since the plan was approved.