MANCHESTER, N.H. —  Presidential hopeful Tom Tancredo said Tuesday he will work against fellow Republicans who support an immigration bill he considers a sellout.

Tancredo aides said the campaign would start a petition drive and volunteer network to help voters campaign against senators who support the White House-backed immigration plan. The bill, which provides a pathway to citizenship to the estimated 12 million illegal immigrants already in the United States, has split Republicans in Congress.

The Colorado congressman announced his "Save America Campaign" hours before he and nine other candidates were to meet for the first Republican debate in the state with the earliest presidential primary.

"I am going to use my presidential campaign as a vehicle to rally the millions of law-abiding Americans who oppose the Kennedy-McCain-Bush sellout of America," Tancredo said in remarks prepared for a news conference outside Republican Sen. Judd Gregg's Manchester office.

Gregg has said he won't decide how to vote on the bill until he has seen all the details in final form.

"This bill grants amnesty to over 15 million illegal aliens," Tancredo said. "It will cost the American taxpayers trillions, bankrupt our Social Security system and speed the day that America becomes a bilingual nation. It does nothing to secure our borders: This bill must be stopped and it must be stopped now."

Most of Tancredo's Republican presidential rivals say the Senate bill amounts to amnesty. Sen. John McCain stands alone among the major Republican candidates in supporting the bill.

"To want the office so badly that you would intentionally make our country's problems worse might prove you can read a poll or take a cheap shot, but it hardly demonstrates presidential leadership," McCain said Monday in Miami.

Also Monday, former Massachusetts Gov. Mitt Romney again criticized the plan — and McCain.

"First, we can and must secure our borders. Second, our country must have an enforceable employment verification system. Third, in reforming our immigration system, we must do so in a way that rewards immigrants who obey the laws and guards against providing special incentives for those who show no regard for them," Romney said.