The U.S. Senate late Monday used a procedural vote (69 to 23) to clear the way for debate on an immigration reform compromise that was announced by a group of senators from both major parties and the White House last week. Prospects for passage of the deal are unclear, as there are opponents on both sides of the political aisle. VOA's Deborah Tate reports from Capitol Hill.

The immigration reform compromise calls for tighter border security and a complex plan to deal with the estimated 11 to 12 million undocumented workers already in the United States as well as future immigrants who want to come to this country to work.

Supporters say the measure offers the best hope to reform the nation's immigration system before next year's congressional and presidential campaigns begin in earnest.

Senators: Edward Kennedy (r) and Robert Byrd (File)

Senator Ted Kennedy, a Massachusetts Democrat, is urging Senate passage of the measure.

"This bill accomplishes our core goals: It provides tough, new enforcement at the border and the work site," said Ted Kennedy. "It allows a realistic path to family security and eventual citizenship for millions of men, women and children already here, and it provides a new system for allocating visas in the future that stresses family reunion and national economic needs."

But there are critics on both sides of the political spectrum.

Many Republicans oppose a provision that would grant undocumented workers legal status to live and work in the United States once they obtain a four-year, renewable "Z visa".

They say the provision amounts to rewarding immigrants who cross U.S. border illegally.

Senator Jim Bunning is a Kentucky Republican:

"No matter what you call it, X, Y, or Z visas, this bill will grant amnesty to millions of illegal immigrants all over this country," said Jim Bunning.

Under the compromise, "Z visa" holders could get on a path toward permanent residency and possible citizenship after meeting certain conditions, including paying fines and learning English. Heads of households would have to return to their home countries first.

Many Democrats are critical of the provision to create a temporary guest worker program, which would allow immigrants to come to the United States to work for up to two years. Such immigrants could renew their terms twice, but only after returning to their home countries for a year each time and without a chance to gain legal residency.

Senator Patrick Leahy, a Vermont Democrat, opposes the provision:

"It risks the creation of a permanent, revolving underclass of workers with limited rights," noted Patrick Leahy. "The temporary worker program, with no opportunity to share in the promise in America, creates an incentive for overstays, and risks creating a new population of undocumented individuals."

Senate Majority Leader Harry Reid, a Nevada Democrat, shares Leahy's concerns, but calls the compromise "a starting point" to debate immigration reform.

The Senate is expected to vote on the measure after the lawmakers return from a week-long recess in June.

The House of Representatives is to debate immigration reform later this year.