High-tech companies looking to bring more skilled workers to the U.S. pushed Monday for more concessions in an immigration bill pending in the Senate. Labor unions said the Silicon Valley had already gotten enough in the legislation and further changes risked chipping away at protections for U.S. workers.

The clash is set to play out in a Capitol Hill hearing room this week as the Senate Judiciary Committee resumes consideration of amendments to sweeping legislation remaking the nation’s immigration system.

At issue are the highly sought-after H-1B visas that allow companies like Google and Microsoft to bring workers to the U.S. to fill job openings for engineers, computer software experts, and other positions where employers say there’s a shortage of U.S. workers. The legislation increases the number of these visas that are available but also adds in a number of restrictions designed to ensure U.S. workers get a first shot at jobs.

Those protections were championed by Sen. Dick Durbin, D-Ill., a Judiciary Committee member who’s also part of the bipartisan “Gang of Eight” senators who authored the immigration legislation.

But high-tech companies have their own champion on the Judiciary Committee: Republican Sen. Orrin Hatch of Utah, who’s prepared a slew of amendments to help their cause.

Hatch is seen as a potential swing vote on the immigration bill, so backers of the legislation, who are working assiduously to ensure their bill passes the Senate with as many votes as possible, would like to court his support. But Durbin opposes Hatch’s efforts and he and other Democrats are under pressure from organized labor not to go along.

“We deemed the current language in the bill to be the compromise. After all, high tech got an awful lot of what it wanted, including the visa limit going up nearly threefold,” said Tom Snyder, immigration campaign manager for the AFL-CIO. “Now they want to compromise the compromise.”

Robert Hoffman, senior vice president for government affairs at the Information Technology Industry Council, disagreed. He said that the changes sought by Hatch, whose state is increasingly becoming a major high-tech employer, mostly amount to mechanical fixes to ensure the high-tech provisions work to boost economic growth and job creation in the U.S.

“It’s very important that the H-1B be workable, and I think that’s what we’re trying to fix,” Hoffman said. “Because the reality is the legislation as drafted in our view runs the risk of pushing work and investment that could come through temporary visas outside the United States.”

The Information Technology Industry Council joined dozens of other business groups and state and local chambers of commerce and technology councils in sending a letter to Judiciary Committee members Monday outlining their concerns about the high-tech language in the bill.

The bill would raise the cap on H-1B visas from the current 65,000 annually to 110,000, with the potential to adjust upward to 180,000 depending on how many visa applications are received and what the unemployment rate is. High-tech companies said the unemployment rate shouldn’t be a factor because it might not reflect actual demand for skilled workers. Hatch has an amendment to make that change.

The Judiciary Committee meets today, but the consideration of the bulk of Hatch’s amendments looked likely to be put off until Thursday to give senators time to see if they could reach a resolution.