U.S. nuclear energy firm Westinghouse Electric Company filed a suit against South Korean state firms competing for a nuclear reactor deal with Poland.

According to industry sources on Monday, Westinghouse filed a suit in U.S. federal court on Friday against Korea Hydro and Nuclear Power(KHNP) and Korea Electric Power Corporation(KEPCO) seeking to block the export of the APR1400 nuclear reactor by KHNP.

In the legal filing, Westinghouse claims that KHNP’s APR1400 reactor design includes intellectual property licensed by Westinghouse and requires its permission before being transferred to Poland.

The lawsuit reportedly comes amid media reports that the Polish government was preparing to sign a preliminary agreement for nuclear reactors with KHNP instead of Westinghouse. The two companies are the leading bidders for the nuclear project.