Silicon Valley has wasted no time in weighing in. Executives have called senators to press their case, industry lobbyists say. And those lobbyists have themselves been on hand when the committee has taken up their issues, ready to huddle with Senate aides during breaks.

As if to underscore the industry’s concern in passing the bill, the secretary of homeland security, Janet Napolitano, traveled to San Francisco on Friday to discuss revamping the immigration law with technology executives.

Critics of Silicon Valley counter that its demands could imperil the overhaul as a whole, including the fate of millions of migrants who stand to gain legal papers.

How can the tech companies threaten to kill comprehensive legislation “when it contains almost all they have said they wanted?” said Bruce Morrison, a former chairman of the House immigration committee who now lobbies for the Institute of Electrical and Electronics Engineers. “All of America should lose the good the bill does so that they can fire Americans and replace them with H-1Bs? Ridiculous.”

The industry is unlikely to actively sabotage the bill if it does not get its way. It could, though, stop supporting the cause, as it has enthusiastically done this year. A well-financed group led by Facebook’s chief executive, Mark Zuckerberg, has backed television advertisements for Republicans who support the immigration overhaul. A “virtual march” is planned for Wednesday; the event is intended to mobilize tech employees to bombard Congress with automated messages in favor of the bill.

The draft bill makes it easier to sponsor foreign math and science graduates from United States universities for permanent residency. It creates a visa program for entrepreneurs. And it expands, to 110,000, from 65,000, the number of temporary workers allowed into the country every year on H-1B visas, in addition to several thousand more when there is additional demand for workers.

“Over all, tech has gotten, by any metric, the best bill they’ve ever seen on this issue in terms of H-1Bs,” said an aide to the Judiciary Committee, who spoke on the condition of anonymity because negotiations were continuing.