NEW YORK – The battle over J.C. Penney’s future just got uglier.

Activist investor Bill Ackman said Friday that he has lost confidence in J.C. Penney’s board and that its chairman should be replaced. Penney Chairman Thomas Engibous fired back and called Ackman’s comments “inaccurate and counterproductive.”

The exchange adds more fuel to an unusually public squabble between Ackman and the rest of J.C. Penney’s board over how quickly it should replace CEO Mike Ullman. Ackman’s investment firm, Pershing Square Capital, has a nearly 18 percent stake in Penney and he sits on the company’s board of directors.

Meanwhile, investment firm Perry Capital, which owns 7.26 percent stake in Penney, came out in support of Ackman in a letter released in a regulatory filing and urged the board for a change in management.

The disagreement is over how long it will take to find a new CEO for J.C. Penney. Ackman says the process should take 30 to 45 days. The board has said Ullman is the right person for the job for now.

The fight could be a distraction as Penney tries to undo the damage done to its business by a failed makeover spearheaded by its previous CEO.

Analysts had expected Ullman’s reign the second time around would be transitional until Penney hired a replacement.