U.S. regulators should reject the PJM Interconnection’s proposal to change its capacity market rules during an auction, in part because it would undermine certainty in wholesale power markets, according to power plant companies including Constellation Energy (NASDAQ:CEG), NRG Energy (NYSE:NRG) and Vistra (NYSE:VST) as well as generator and clean energy trade groups, UtilityDive.com reported Monday.

PJM’s proposal issued last month amounts to “after-the-fact tinkering” that is barred by the filed rate doctrine and the rule against retroactive ratemaking, the Electric Power Supply Association said in a filing at the Federal Energy Regulatory Commission.

The American Clean Power Association, the Solar Energy Industries Association and Advanced Energy United jointly protested PJM’s proposal, calling it a “drastic” overreach.

If PJM’s proposal is approved, it would set a precedent that any regional transmission organization can change capacity market auction results if the grid operator disagrees with the outcome, the groups said.

Constellation (CEG) is one of two utilities named to Goldman Sachs’ list of “50 top return-on-equity stocks for a tough ROE year.”