For decades, relatives of immigrants already in the United States have had preference among people wanting to immigrate to the U.S.
But now, the White House and senior Republican lawmakers want to strictly limit the arrivals of family members, instead giving preference to skilled workers sought by employers.
Democrats say that is impractical and inhumane.
"It would be a huge mistake to expand employment-based immigration at the expense of our historic tradition of family-based immigration," Senator Edward Kennedy, one of the key negotiators, said this week.
The issue has become "one of the most contentious" in pulling together a broad immigration bill upon which Republicans and Democrats can agree, Kennedy said. The idea is to give many of the United States' estimated 12 million illegal immigrants a chance at citizenship and create a guest-worker program for new arrivals.
Nearly two-thirds of legal permanent residents admitted last year were family-sponsored immigrants, while less than 12.6 percent came in based on employment preferences, according to the U.S. Department of Homeland Security. Roughly one-fourth fell into other categories, such as refugees and aslyum seekers.
Under the White House proposal, legal immigrants would lose the right to petition to bring adult children and siblings to the U.S. They could do so for spouses and minor children, but their ability to sponsor parents would be severely limited.
The proposal would limit or end preferences for people who had family members living legally in the U.S., and award many more visas based on employability criteria, such as education and skills.
Temporary workers could not bring family members at all unless they met a certain wealth threshold and had health insurance.
Reshaping immigration laws is a priority for President George W. Bush, who wants it as part of his domestic legacy. It also would be a popular achievement for Democrats to take to voters in the next election.
Senate Democratic leaders have promised to bring up a measure, with or without Republican agreement, within two weeks.
"I will work with both Republicans and Democrats to get a bill to my desk before the summer is out, hopefully," Bush said.
Religious groups and Asian-American advocacy organizations are among the strongest opponents of the proposed changes.
Karen Narasaki of the Asian American Justice Center said the proposal to do away with family-based visa preferences is "a cold calculation about numbers. They're trading off families for employers."