WASHINGTON (AP) — 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.

High-tech companies also are concerned about a new provision requiring them to show they've tried to recruit U.S. workers before hiring anyone on an H-1B visa. Hatch would limit the requirement only to companies that are more heavily dependent on H-1B visas, so that it wouldn't apply to a number of U.S. tech companies.

Hatch also has an amendment to change a requirement in the bill seeking to ensure that U.S. workers are not displaced by the hiring of foreigners.

The Judiciary Committee meets Tuesday, 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.

Durbin and the three other Gang of Eight members on the Judiciary Committee — Sens. Chuck Schumer, D-N.Y., Lindsey Graham, R-S.C., and Jeff Flake, R-Ariz. — have resolved to vote together to defeat changes that would strike at core provisions of the bill and threaten the coalition backing it. But it was unclear Monday whether the lawmakers would be able to reach a compromise that could accommodate Hatch in a way Durbin could go along with. There was also no indication that Hatch would commit to supporting the bill even if his amendments on high-tech issues were accepted, because he's raised a number of other concerns as well.

Meanwhile the committee on Tuesday planned to turn to several amendments from Sen. Charles Grassley, R-Iowa, who's supporting even greater restrictions on H-1B visas that those in the bill, but it seemed unlikely his efforts would prevail.

Beyond the H-1B provisions, the legislation makes changes favorable to the high-tech community that reflect the industry's increased lobbying muscle on Capitol Hill, as well as concerted involvement during the bill-writing process. The bill exempts certain immigrants, including those with advanced degrees in science, technology, engineering or math from U.S. schools, from annual limits on the permanent resident visas known as green cards. It also creates a new visa for foreign entrepreneurs coming to the U.S. to start companies.

In the latest sign of involvement by the high-tech and business communities, New York Mayor Michael Bloomberg's Partnership for a New American Economy, a group made up of business leaders and mayors, was to announce plans Tuesday for a "virtual march on Washington" to get people to use social media platforms to push Congress to support the immigration bill. The effort, set for next week, is to be co-chaired by Organizing for Action, a group headed by loyalists to President Barack Obama, and Republicans for Immigration Reform, led by former Bush administration Commerce Secretary Carlos Gutierrez.

Overall, the legislation would aim to boost border security, require all employers to verify the legal status of their workers, allow tens of thousands of new high- and low-skilled workers into the U.S., and create an eventual path to citizenship for the approximately 11 million already here illegally. It is a top second-term priority for Obama.