WASHINGTON (Reuters) - A U.S. appeals court on Friday vacated a trial court's decision to certify a class action against railroad companies, a procedural win for the companies in a case about whether they illegally colluded to fix the price of fuel surcharges.

A unanimous panel of the U.S. Court of Appeals for the District of Columbia Circuit sent the lawsuit back to the trial court to reconsider the matter in light of a recent U.S. Supreme Court decision about class actions.

Thousands of freight-shipping customers are suing four major railroad companies over the alleged conspiracy. They are seeking potentially billions of dollars in damages.

Last year, the trial court agreed to hear the shipping customers' claims as a class action, but then in March, the U.S. Supreme Court ruled in a separate case that judges should carefully review the economic model for how damages would be calculated before they certify a class.

The high court's ruling commands "a hard look at the soundness of statistical models," something the trial court "never grappled with," Judge Janice Rogers Brown wrote for the three-judge appeals panel.

The defendants in the case are Berkshire Hathaway Inc's BNSF Railway Co and units of Union Pacific Corp , CSX Corp and Norfolk Southern Corp . They did not immediately respond to requests for comment.

(Reporting by David Ingram; Editing by Gerald E. McCormick and Lisa Von Ahn)