Latham & Watkins can proceed as lead trial counsel for a defendant in a massive antitrust class action, a Washington federal district trial judge ruled on Tuesday, denying a motion to disqualify the firm.

Latham represents Union Pacific Railroad Co., one of four U.S. freight rail companies accused of conspiring to raise customer rates through fuel surcharges. After Latham entered the multidistrict litigation last fall, several now-ex-clients who were unnamed class members—petroleum byproducts distributor Oxbow Carbon LLC and its subsidiaries—moved to disqualify the firm, arguing it suffered a conflict of interest.