The groups say the plant should be blocked until federal regulators approve safety changes prompted by last year's nuclear disaster in Japan.
Twelve groups, including the Southern Alliance for Clean Energy, say they prepared the suit Thursday and expect it to be filed no later than Friday in the U.S. Court of Appeals in Washington.
The Nuclear Regulatory Commission voted 4-1 last week to issue a permit to Atlanta-based Southern Co. to build and operate two new reactors at its Plant Vogtle site south of Augusta.
The NRC last approved construction of a nuclear plant in 1978.
