In preparation for a momentous and rare joint appearance before Congress, four titans of the tech industry turned to prominent lawyers in Washington for counsel to prepare for a hearing that will unfold against the backdrop of investigations by federal law enforcement agencies.

The chief executives of Amazon, Apple, Facebook and Google are set to appear Wednesday before a U.S. House of Representatives panel for a hearing that will mark the culmination of a 13-month congressional investigation of antitrust issues involving the tech sector.