The bill would require the state regulatory commission to look at the contract again if the state Supreme Court does not uphold it.
The Rockport plant would take coal and process it into various substances, including synthetic natural gas, which burns just like traditional natural gas.
The agreement requires Duke Energy to absorb nearly $900 million for the construction its Edwardsport coal gasification plant.
The plan has natural gas customers paying the difference if the state fails to make a profit off of natural gas purchases.
Duke Energy officials say they have nearly all the factors in place to burn synthetic gas—the main component in the gasification process.
Once completed, Indiana will sell energy from the coal gasification plant in Rockport even if there are cheaper options.