National advocates for immigrant rights are hammering Mitt Romney this week for opposing legislation providing a path to citizenship for illegal immigrant students.

The advocates maintain that Romney's recent vow to veto the DREAM Act if he wins the White House will "disqualify" him in the eyes of Latino voters, an ever-growing constituency that both parties have sought to court.

"Millions of Latino voters see their own children and family histories in the aspirations and ambitions of the DREAM youth and don’t take kindly to those determined to slam the doors of opportunity in their faces," Frank Sharry, executive director of America’s Voice, an immigrant rights group, said Tuesday in a statement.

"If he becomes the Republican nominee, Romney will find it virtually impossible to reach the 40 percent threshold among Latino voters that Republican candidates need to win the White House," Sharry said.

While campaigning in Iowa on Saturday, Romney didn't minced his words when asked how he would approach the DREAM Act as president.

"The question is, if I were elected and Congress were to pass the DREAM Act, would I veto it, and the answer is yes," Romney said. "For those that come here illegally, the idea of giving them in-state tuition credits or other special benefits, I find to be contrary to the idea of a nation of laws."

The reference to in-state tuition credits was a shot at Texas Gov. Rick Perry, another GOP presidential hopeful, who's taken fire from conservatives for signing legislation allowing undocumented immigrants to receive in-state tuition rates at public colleges and universities.

"If I'm the president of the United States, I want to end illegal immigration so that we can protect legal immigration," Romney added. "I like legal immigration."

Sharry said the remarks, while intended to woo Iowa conservatives in the run-up to this week's caucuses, will make it much tougher for Romney to win vital swing states with significant Hispanic populations, including Arizona, Colorado, Florida, Nevada and New Mexico.

“Romney’s comments about the DREAM Act will disqualify him among a large swath of Latino voters throughout the nation," Sharry said.

A topic of fierce debate in recent years, the DREAM Act would carve a pathway to permanent residency – and ultimately citizenship – for certain students brought to the U.S. illegally by their parents. To qualify, they must have been in the country for at least five years; have earned a high school diploma or its equivalent, and enter an institution of higher education or the military.

Supporters say the bill would empower motivated young people to develop skills that could benefit the entire country. Opponents, on the other hand, argue that those living illegally in the country — even those brought involuntary as kids — should be treated as criminals, not rewarded with amnesty and benefits.

Backed by President Obama, Democratic leaders ushered the DREAM Act through the House in late 2010, but Republicans and centrist Democrats killed it in the Senate.