U.S. Senator Elizabeth Warren has a new target: the biggest sellers of annuities and the diamond-encrusted rings, iPads, stock options and cruises she says they’re using to entice brokers to sell their investments.

Warren, the Massachusetts Democrat and prominent critic of Wall Street, is planning to send letters Tuesday to the U.S.’s 15 largest annuity providers, her office said. She wants to know whether perks they provide encourage brokers to put personal interests ahead of the retirement goals of clients.

“I am concerned that these incentives present a conflict of interest for agents and financial advisors that could result in these agents providing inadequate advice about annuities to investors and selling products that may not meet the retirement investment needs of their buyers,” Warren said in the letters, which were slated to go to companies including Prudential Plc’s Jackson National Life, American International Group Inc. and Lincoln National Corp.

$235 Billion

In the letters, Warren said car leases, National Football League Super Bowl-style rings and other perks are widely known in the industry and appear to be “kickbacks directed at annuity agents and brokers.” Warren’s office is asking the companies to provide by May 11 a list of all incentives offered to middlemen.

Warren is latching onto incentives in the $235 billion market for annuities to build support for proposed Labor Department regulations that require brokers to act in their retirement clients’ best interest, a standard known as a fiduciary duty. The proposal issued this month is expected to face stiff opposition from Wall Street, Republicans and some Democrats.