The accounting industry’s main trade group on Monday pushed back against federal regulators who are again scrutinizing big accounting firms’ policies of requiring mandatory retirement ages for their partners.

The rebuke comes after the Equal Employment Opportunity Commission investigated one firm, PricewaterhouseCoopers LLP, over its policy that requires its partners to retire by age 60, with a view toward whether the policy constitutes age discrimination. The EEOC ultimately decided last year not to bring a case against PwC...