Senator Marco Rubio (Gage Skidmore)

Advocates of more lenient immigration policies say they feel more optimistic than ever that Congress will pass legislation that will help millions of undocumented immigrants eventually become U.S. citizens.

But their optimism, sparked by a bipartisan immigration reform proposal by eight of the U.S. Senate’s most influential members—four Republicans and four Democrats—to be unveiled Monday afternoon, also carries concerns and questions.

“There’s momentum this time around,” said Kica Matos, Director of Immigrant Rights and Racial Justice at the Center for Community Change in New Haven, Conn.

Immigration-restriction groups acknowledged immigrant advocates are riding a wave now—but they vowed nonetheless to fight what they deem is a veiled, large-scale amnesty.

Latinos turned out in record numbers to vote in the presidential election in November—with 7 out of 10 voting for President Barack Obama.

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Their overwhelming support for the president was attributed in great part to the harsh rhetoric on immigration by many Republicans, especially during the GOP primaries last year. Obama is expected to unveil his own plan for comprehensive immigration reform on Tuesday in Las Vegas—the move prompted senators to move quicker than expected this week to beat the president’s announcement, according to published reports.

“We have senators, we have the president unveiling his plan tomorrow, and the grassroots is gearing up to move this forward this year,” Matos said. “And consensus is on our side—a growing number of Americans realize this broken system has led to 11 million people in this country without documents. We have a mess on our hands, we need to fix it.”

Groups that favor strict immigration enforcement assailed the plan to give undocumented immigrants a path to legalization—reserving particularly harsh criticism for Republican senators—including Florida’s Marco Rubio—as sell-outs.

“The plan is supposedly the result of three years of closed door negotiations by a group of pro-amnesty senators,” said a statement by the Federation for American Immigration Reform, or FAIR, the country’s leading anti-illegal immigration lobby group,  “without any input from the American people or any examination of how amnesty or the continued expansion of legal immigration at all levels affects the U.S. labor market.”

Read the full article on FOX NEWS Latino.