RIYADH—Foreign workers in Saudi Arabia stayed away en masse from their offices, schools, stores and other workplaces on Monday as the government mounted a crackdown on illegal residents.

Authorities in Saudi Arabia—the biggest labor market in the Persian Gulf, and home to an estimated two million to three million illegal foreign workers—have raided office buildings and set up document checkpoints on main roads recently for workers here illegally, according to workers, Saudis and media reports.

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