A public battle between struggling US retailer JC Penney and activist shareholder William Ackman is starting to heat up.

The retailer's board is considering taking action against Ackman, after the Pershing Square hedge fund manager publicly released confidential boardroom deliberations, the Wall Street Journal reported, citing unnamed sources close to the matter.

The dispute centres around Ackman's decision to make public a letter calling on the board to move more quickly to replace interim chief executive Myron Ullman.

JC Penney chairman Thomas Engibous responded by saying that the retailer's board is focused on stabilising and rejuvenating the business.

"It is following proper governance procedures and members of the board have been fully informed and are making decisions as a group. This includes the CEO search process, which is being conducted at an appropriate pace. The board also continues to actively oversee management as it conducts the important work underway to rebuild the company," said Engibous.

"Ackman's statements are misleading, inaccurate and counterproductive."

In a prior statement, Engibous emphasised that the company has made significant progress since Ullman's appointment four months ago, and that he has led significant actions to correct the errors of previous management and return the company to sustainable, profitable growth.

Engibous said: "When Mike returned, it was understood that there would be an effort to rebuild the management team, including a search process to identify his successor.

"The CEO search process, which began in earnest three weeks ago, will be careful and deliberate to ensure we find the right long-term leader for JC Penney. In the meantime, Mike and the leadership team will continue the work under way to improve the company's performance and get back on a path to profitable growth."