JEFF AMYJACKSON, Miss. (AP) â¿¿ Opponents will return to court Friday seeking to again invalidate state regulators' decision to allow Mississippi Power Co. to build a $2.8 billion power plant in Kemper County. The Sierra Club and other opponents of the plant want Harrison County Chancellor Jim Persons to rule that the new permission granted by the Mississippi Public Service Commission in April was illegal. Opponents say the PSC should have held new hearings after the state Supreme Court rejected the original certificate in March. The high court ruled that the commission hadn't adequately laid out its reasons for raising the cost cap on the plant from $2.4 billion to $2.88 billion in 2010. New hearings could have considered, among other things, how much lower natural gas prices are now than when the plant was first approved, said Sierra Club state Director Louie Miller. "A lot has changed since we had the initial hearings," he said. Opponents argue that it's not too late for Mississippi Power, a unit of Atlanta-based Southern Co., to stop building the part of plant that's supposed to convert soft lignite coal into a gas that would be burned to generate power. The Sierra Club opposes it because it says burning coal will contribute to global warming, even though the plant plans to capture carbon dioxide and pipe it to oilfields to be injected into the ground. Miller also argues that Kemper's technology is unreliable, citing a Mississippi Power official who told the PSC under oath that he couldn't guarantee the plant would work. "Is Kemper the cheapest and is it the most reliable?" Miller asked. "Kemper is neither, by a country mile." Mississippi Power, though, is steadfast that lignite is the right power solution, saying building the plant next to the lignite mine will cut costs. The company also says it is important to not become overly reliant on natural gas, in case prices rise. Kemper, along with a new nuclear plant Southern Co. is building near Augusta, Ga., represent the company's response to tightening restrictions on traditional coal-burning plants. The Kemper County plant will be named after former Southern Co. CEO David Ratcliffe, under whom that strategy was developed.