U.S. Senators Elizabeth Warren (D-MA.), Sherrod Brown (D-OH) and Chris Van Hollen (D-MD) are calling on the Securities and Exchange Commission to overhaul insider trading rules that they claim put retail investors at a disadvantage.

The trio, all members of the Senate Committee on Banking, Housing, and Urban Affairs, sent a letter to the SEC last week urging the regulator to review and consider reforming policies regarding 10b5-1 plans. The policy allows corporate executives to schedule stock purchases and sales for the purpose of avoiding instances of insider trading. Yet the group of lawmakers suggests executives — particularly those in the healthcare sector — are misusing the plans for personal profits.

The SEC created the 10b5-1 “safe harbor” in 2000 to allow corporate executives, who often have continuous access to material nonpublic information, to sell their holdings without engaging in insider trading. Research, however, suggests that initial trades set up by 10b5-1 plans often appear to be based on material nonpublic information, and executives can and do modify or cancel their plans in response to inside information to increase their own profits, the lawmakers wrote.

They pointed to a December working paper in the Social Science Research Network journal alleging that public companies, particularly mid-cap firms and those in the healthcare sector, proportionately disclose positive news on days when corporate executives sell shares under predetermined 10b5-1 plans.

“In addition to harming ordinary investors, the abuse of 10b5-1 plans and the short-term, windfall profits obtained by insiders through abuses of these plans undermine public confidence in open, fair markets and the products they create,” the senators said. They suggested that the SEC enforce a four-to-six month “cooling off period” between when trades are planned or rescheduled and when they’re executed. The agency’s previous chair recommended such a period but the SEC hasn’t yet adopted it, according to an article Friday in Business Insider.