SAN FRANCISCO — Turning back the pleas of four Silicon Valley giants, the Ninth Circuit refused Tuesday to intervene in a class action that alleges the companies conspired not to poach each others’ employees.

In a brief order, the court turned down Google, Apple, Intel and Adobe Systems’ petition for interlocutory review of U.S. District Judge Lucy Koh’s order last October certifying a class of some 64,000 employees.