The Appeals Board said the Illinois EPA had not given the public sufficient opportunity to comment prior to the final ruling earlier this year.
On January 17, the Illinois EPA awarded the plant a prevention of significant deterioration permit.
"It appears to be a procedural issue regarding the state, and we would expect to resolve it in a timely manner," a Peabody spokeswoman told Platts.
The 1500MW plant will be fueled by six million tons of coal produced each year from an adjacent mine. Construction is planned for later this year.
