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 today 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.”

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