The Sierra Club of Mississippi is arguing in court that Mississippi Power Co. should assume the risk of building a new coal power plant, rather than customers, while an appeal trying to stop the project goes through the courts.

“If Mississippi Power thinks it is such a good idea to build this boondoggle, the company should take the risk and build the plant on its own nickel,” Sierra Club attorney Robert Wiygul said. “Instead, Mississippi Power wants the ratepayers to take all the risk.”

The Mississippi Public Service Commission voted Tuesday to give new approval for the coal-fired power plant in Kemper County, pushing aside opponents’ calls for a fresh look at the plant’s finances.

The commission voted 2-1 to approve the $2.4 billion plant. Southern District Commissioner Leonard Bentz and Central District Commissioner Lynn Posey, both Republicans, voted for the plant. Northern District Commissioner Brandon Presley, a Democrat, voted against it.

While Presley wrote in a three-page dissent that taking new testimony and evidence would be “an appropriate response” to the court decision, the two other commissioners disagreed. They wrote that the commission had collected volumes of testimony and evidence before initially ruling in favor of the plan.

The power plant would burn lignite mined nearby, convert it to a gas to be burned to generate power and capture carbon dioxide to be pumped underground.

The PSC had to vote for the plant again after the state Supreme Court ruled last month that regulators didn’t fully explain why they raised a cost cap from $2.4 billion to $2.88 billion. The Sierra Club, which opposes the plant, brought the lawsuit that led to that decision.

Commissioners said Tuesday’s ruling does not raise the $2.88 billion cost cap, which is meant to provide a 20 percent margin for overruns.

Mississippi Power spokeswoman Cindy W. Duvall said Thursday that the continued legal action by the Sierra Club was expected.

“We expect this type of activity from the Sierra Club right up until the Kemper Project comes online,” Duvall said. “This is what they are paid to do. No matter that this is the best option for our customers or how environmentally responsible the project is, they will continue to mislead our customers with erroneous information.”

Louie Miller, director of the Sierra Club in Mississippi, said Thursday that the commission’s decision to approve the plant amounted “to little more than putting some lipstick on the pig.” Miller said the opponents have a judge to stay the commission’s action but “whether that keeps Mississippi Power from building depends on how the judge rules.”

Miller said opponents still want a halt to construction at the site, where the unit of Atlanta-based Southern Co. has already spent $1.1 billion and committed another $400 million.

The environmental group opposes the plant largely because it opposes mining and burning coal, saying it produces more carbon dioxide than natural gas. Carbon dioxide contributes to global warming, scientists say.