Exelon Corp. will pay $400,000 for inadvertent power trading violations during its takeover of Constellation Energy Group Inc.

The Justice Department announced the settlement Thursday. A federal judge in Washington will have to approve it before it's final.

Exelon was required to sell three Maryland power plants to settle antitrust concerns about the $7.9 billion Constellation deal. The Justice Department says before the plants were sold, Exelon agreed to sell their power at or below cost to ensure Exelon wouldn't be able to raise electricity rates. The Justice Department says Exelon sold power above cost, but that once it realized the sales had been made, the company notified regulators and returned the profits.

Exelon accepts responsibility for the error and adds it had little impact on the market or customers.