Silicon Valley: Microsoft is shifting high-level work such as the next version of Windows Operating System to foreign contractors, including Indians, a Seattle-based labour union has claimed.

The Washington Alliance of Technology Workers (WashTech) said it has obtained internal company documents that show that Microsoft now employs nearly 2,000 workers in India, double the 970 number it previously acknowledged.

Microsoft, however, disputed the notion, saying it doesn't use contractors for core development.

WashTech alleges the documents show that while Microsoft employs 970 full-time direct employees in India, there are an additional 1,100 people working for the company in India under contracts with outsourcing firms, bringing Microsoft's total presence in the country to more than 2,000 people.

WashTech, which wants to unionize Microsoft employees, is one of the most vocal critics of offshore outsourcing, a hot button in the current Presidential campaign.

The documents include wage lists and projects for Microsoft at Infosys, Wipro, Satyam and Tata Consultancy Services.

The internal documents, WashTech said, suggest that the contractors and employees are involved in high-level development projects and not just low-level work such as call center customer service.

"They clearly have not been forthcoming about the extent of their offshore outsourcing," said Marcus Courtney, WashTech president and organiser.