WASHINGTON — MetLife has been fined $20 million by Wall Street’s policing body for misleading customers in switching them from variable annuities contracts into more expensive ones.

The Financial Industry Regulatory Authority said Tuesday the decision was its largest fine related to variable annuities, popular yet complex investments that have grabbed the attention of regulators in recent years. FINRA has taken hundreds of disciplinary actions against brokers and investment firms for abuses in sales of variable annuities.

FINRA also ordered MetLife Securities Inc. to return $5 million to customers “for making negligent material misrepresentations and omissions” on applications for switching into new variable annuities contracts. Tens of thousands of customers were affected, the regulators said.

New York-based MetLife neither admitted nor denied the allegations.

“MetLife fully cooperated with the FINRA investigation and we are pleased to put this matter behind us,” the company said in a statement.

FINRA said that from 2009 through 2014, MetLife misrepresented or omitted one important fact related to the costs and guarantees of customers’ current variable annuities contracts in 72 percent of the 35,500 replacement applications it approved. The company told customers that their current contract was more expensive than the recommended replacement, when in fact the current contract was less expensive, according to the regulators.

In addition, MetLife failed to tell customers that the recommended new contract would reduce or eliminate important features of the current contract, such as guaranteed income benefits and accrued death benefits.

MetLife’s variable annuities replacement business garnered it around $152 million in commissions over the period, FINRA said.

Sales of variable annuities, which are tax-deferred and often used to save for retirement, have ballooned in recent years. They are contracts with investors in which the company selling them agrees to make periodic payments to the investor.