A group of cleaners employed by a contract cleaning company used by Google is threatening to strike over what they allege are poor working conditions at its London offices, reports Business Insider. The cleaners, who work for London-based contract cleaning firm Principle, allege that their employer has withheld bonus payments, refused to provide contractual sick pay, and drastically cut the workforce at Google's offices, effectively doubling their workload. Their concerns highlight the growing frustration caused by Google's heavy reliance on contract workers, creating a two-tier workforce in which many are locked out of the company's perks and benefits. The cleaners are publicly calling on Google to take action, but a Google spokesperson says compensation and benefits are all determined by the contractor firm. According to a report from the New York Times, Google employs approximately 121,000 temps and contractors versus 102,000 full-time workers.