The report, released Tuesday by environmental group Friends of the Earth and anti-subsidy group Taxpayers for Common Sense, says members of Congress could try to enact changes before year's end as part of a larger tax bill.
Mississippi Power isn't immediately responding to a request for comment.
The $7 billion plant has already received $400 million in federal aid. However, Atlanta-based parent Southern Co. repaid $400 million tax credits after the plant missed startup deadlines.
Provisions under discussion are meant to encourage plants, like Kemper, that burn coal and capture carbon dioxide. Opponents say Kemper's huge cost proves such projects are flawed.