The accounting firm KPMG has fired six employees, including the head of its audit practice in the United States, after it learned they were given improper warnings ahead of planned audit inspections by its regulator, the Public Company Accounting Oversight Board.

KPMG said that an individual who had joined the firm from the Public Company Accounting Oversight Board had received confidential information from an employee of the oversight board and shared it with others at KPMG.

“That information potentially undermined the integrity of the regulatory process,” KPMG said in a news release on Tuesday. The accounting firm said it had learned of the matter from a whistle-blower in February.

An investigation by an outside law firm determined that these individuals either had improper warnings of audit engagements to be inspected by the oversight board, which polices auditors in the United States, or were aware that others had received such warnings and had failed to properly report the situation in a timely manner, KPMG said.