James Maiwurm, Squire Sanders’ chairman, was waiting for a flight at National Airport in Washington, D.C., at 9 in the morning on May 22 when his cellphone rang. On the line was a D.C. partner with alarming news: Someone was subverting the firm’s plans to merge with Patton Boggs. Specifically, former clients of Patton Boggs were challenging a settlement that Patton and Chevron Corporation struck over fraud allegations related to Patton’s role in bringing a multibillion-dollar suit against the oil company in Ecuador.

The call came at a particularly awkward moment: Squire partners were in the final hours of a three-day vote on a merger with the D.C. firm. If Patton Boggs’ former clients convinced a judge to reopen the settlement, that firm would face renewed litigation and the potential for a much larger financial hit—and in a merged firm, so would legacy Squire partners.