Work permits and intra-company transfers from India to the U.S. are trade issues and should not be confused with immigration issues, India's NASSCOM (National Association of Software and Service Companies) in Delhi said late Tuesday.

NASSCOM was reacting to letters written by U.S. Senators Chuck Grassley, an Iowa Republican, and Richard Durbin, an Illinois Democrat, to nine Indian companies asking for details on their use of the H-1B visas. The nine companies account for close to 20,000 visas, the senators said on their Web sites. The companies include India's top outsourcers, Tata Consultancy Services, Infosys Technologies, and Wipro.

More and more, it appears that companies are using H-1B visas to displace qualified, U.S. workers, Grassley said in a statement Monday. "Now, as we move closer to debate on an immigration bill, I continue to hear how people want to increase the number of H-1B visas that are available to companies," he said.

Work permits are primarily a tool to facilitate trade and allow global companies to bring key staff to the U.S. on temporary assignments, just as U.S. staff often travel across the world for temporary assignments, and this is clearly different from immigration, NASSCOM said.

Grassley and Durbin introduced legislation in April that they said aims to give priority to U.S. workers and crack down on unscrupulous employers who deprive qualified U.S. citizens of high-skill jobs.

The H-1B visa is an employer-sponsored, nonimmigrant work visa for a foreign worker coming temporarily to the U.S. in a specialty occupation.

The issue of H-1B and L-1 visas is important to India's outsourcing industry as it has a large proportion of staff working on-site on client's projects in the U.S. Indian outsourcing companies as well as U.S. technology companies, have been demanding an increase in the number of H-1B visas allowed in a year, which are currently capped at 65,000.

The Indian outsourcers Grassley and Durbin wrote to were not willing to comment on the letters.

NASSCOM on Tuesday repeated its demand for an increase in H-1B visas. Both U.S. and Indian companies have repeatedly stressed the need to raise the H-1B visa cap, which was reduced from 195,000 to 65,000 two years ago, it said. Constraining the supply when demand is high gives rise to problems for U.S. companies and Indian IT companies, the association added.