Axa SA’s U.S. unit was fined $20 million by a New York regulator for making changes to a retirement product without fully informing the watchdog.

Axa Equitable changed the investment strategy for some variable annuities sold earlier, limiting potential returns for customers without providing adequate notice to regulators, the New York Department of Financial Services said yesterday in a statement.

“Axa changed the rules on these important products midstream,” Superintendent of Financial Services Benjamin Lawsky said in the statement. “When it comes to retirement products, insurers must go above and beyond to explain any changes that would alter investor returns.”

Axa said in a statement that it routinely makes changes to products and that policyholders have a “full menu” of investment options. The company said the regulator found that it “should have communicated better to NYDFS when it made certain technical filings.”

Variable annuities can guarantee that a client’s account will appreciate even if assets decline in value. Axa, based in Paris, applied a strategy called Axa Tactical Manager to some accounts, which was designed to smooth returns in volatile markets, DFS said.