HOUSTON- Two U.S. shale producers have challenged an energy pipeline operator's proposed surcharge for the Trump administration's 25% tariff on imported steel, raising the stakes for pipeline builders facing higher construction costs.

The United States imposed tariffs on imported steel and aluminum last year to shield U.S. producers from overseas competition. U.S. energy industry trade groups have warned the tariffs could raise costs for companies and consumers.

U.S. oil producer ConocoPhillips COP.N and a unit of Canadian producer Encana Corp on Monday asked the Federal Energy Regulatory Commission to reject Plains All American Pipeline's proposed tariff surcharge on its Cactus II oil pipeline, according to a regulatory filing.

Houston-based Plains this month proposed charging shippers a 5 cents per barrel fee on its 670,000 barrel-per-day (bpd) Cactus II pipeline next April to offset higher construction costs due to the steel tariffs. 

ConocoPhillips, Encana and Plains did not immediately respond to requests for comment.

(Reporting by Collin Eaton Editing by Chizu Nomiyama and David Gregorio) ((Collin Eaton@thomsonreuters.com; +1 713-210-8509;))