CASPER, Wyo. (AP) — Petroleum retailers are suing the Wyoming Department of Transportation and a western Wyoming school district for selling compressed natural gas as fuel.

The Colorado Wyoming Petroleum Marketers Association argues that against Sublette County School District 1 in Pinedale is improperly competing with private business. The Associated Press reports that the petroleum marketers believe tax dollars are being used to compete against the private industry.

Earlier this year, the state transportation department licensed the school district to sell compressed natural gas to the public. Compressed natural gas is a cleaner and cheaper alternative to gasoline.

A school district official told the paper that the district is not giving much competition to private petroleum retailers and wholesalers.