WASHINGTON (AP) — To the U.S. technology industry, there's a dramatic shortfall in the number of Americans skilled in computer programming and engineering that is hampering business. To unions and some Democrats, it's more sinister: The push by Facebook's Mark Zuckerberg to expand the number of visas for high-tech foreign workers is an attempt to dilute a lucrative job market with cheap, indentured labor.

The answer is somewhere in between, depending as much on new technologies and the U.S. education system's ability to keep up as on the immigration law itself. But the sliver of computer-related jobs inside the U.S. that might be designated for foreigners — fewer than 200,000 out of 6 million — has been enough to strain a bipartisan deal in the Senate on immigration reform, showcase the power of big labor and splinter a once-chummy group of elite tech leaders hoping to make inroads in Washington.

"A lot of people agree that employers should have access to (highly trained) immigrants — that they are a benefit to the country, and we are a country of immigrants," said B. Lindsay Lowell, director of policy studies at Georgetown University's Institute for the Study of International Migration. "I think the question is how much of a good thing is good."

The Senate immigration bill — the result of months of quiet negotiations among eight influential senators — is on track to nearly double the number of highly skilled foreign workers allowed to work in the U.S. under what's called an H-1B visa, from 65,000 to 110,000. The number of visas could climb as high as 180,000 depending on the number of applications received and the unemployment rate.

The Senate Judiciary Committee planned to take up the portion of the bill relating to H-1B visas on Thursday, paving the way for an eventual floor vote and setting the tone for debate in the House.

The expansion of H-1B visas is considered the first major victory for Zuckerberg's new nonprofit lobbying organization, FWD.us, which receives financial backing from such big tech names as Bill Gates of Microsoft, Reid Hoffman of LinkedIn and Napster pioneer Sean Parker. In announcing the group, pronounced "forward us," Zuckerberg in April called for changes so that U.S. businesses could attract "the most-talented and hardest-working people, no matter where they were born."

But support for FWD.us appeared to crack this week after the group's subsidiary ran television ads backing Republican senators who support immigration reform but also unpopular environmental programs, including the Keystone XL oil pipeline. Two backers of FWD.us — including PayPal co-founder Elon Musk, who now runs electric-car maker Tesla Motors — pulled their support for the group, and several left-leaning groups, including the Sierra Club and MoveOn.org, protested the ads.

Frustration by some tech leaders was captured on Twitter, where site co-founder Evan Williams linked to a blog post on his new company's website that accused FWD.us of "employing questionable lobbying techniques, misleading supporters and not being transparent about the underlying values and long-term intentions of the organization."

In an emailed statement, FWD.us spokeswoman Kate Hansen said: "We recognize that not everyone will always agree with or be pleased by our strategy — and we're grateful for the continued support of our dedicated founders and major contributors. FWD.us remains totally committed to supporting a bipartisan policy agenda that will boost the knowledge economy, including comprehensive immigration reform."

H-1B visa applications can be complex and often are used when a qualified American candidate can't be found for a specialized job in a specific city. The visa candidate typically costs the company money and time, including extensive paperwork.

The flip side is that once a company is permitted to hire a foreign worker, that employee has little leverage to demand a raise or leave for a company's competitor without putting his or her visa at risk.

Scot Melland, president and chief executive of Dice Holdings Inc., which operates a career website devoted to tech jobs, said Dice.com has more than 80,000 positions posted on its site, which turn over an average of every two weeks. And while his company doesn't track how many jobs result in H-1B visa hires, Melland said he predicts that the number of tech jobs and high salaries available to Americans is likely to grow for some time. He said expanding the H-1B program is necessary, so long as safeguards prevent companies from exploiting foreign workers.

"As long as it's not abused, you're still talking about a small fraction of the tech labor market," Melland said.

Lowell said the number of information technology jobs affected by H-1B candidates is closer to 2.5 million than the broader pool of 6 million computer-related jobs frequently cited by industry. He said this more specialized labor market could become distorted by the Senate's plan to increase the number of legal immigrants overall.

According to a recent report by the labor-oriented Economic Policy Institute, the number of skilled guest workers has increased sharply in recent years while only 1 in 2 U.S. college graduates with high-tech degrees can find a job in their field.

"You have to question why we would want to import an increasing number of foreign workers," said Lowell, who co-wrote the report.