PHOENIX -- The Arizona state House is considering a proposal to criminalize illegal immigrants as trespassers if police have reasonable suspicion to check a person's immigration status and find it lacking.

The tough new proposal is already being challenged for its constitutionality. Opponents cite a 2005 ruling by a New Hampshire judge who dismissed trespassing charges against illegal immigrants, arguing police chiefs in two communities did not have the jurisdiction to apply state laws to a federal issue.

Advocates for immigrant rights also say they fear it could lead to racial profiling that would target Latinos living legally in the state.

"It's almost impossible for it to be applied without relying on racial profiling and without committing egregious errors," said Jennifer Allen, director of the Border Action Network, an immigrant rights group based in southern Arizona.

But supporters say the measure wouldn't encourage racial profiling because officers would still need probable cause to believe that people violated the law before they could arrest them.

Some of Arizona's police forces have already established rules for enforcing federal immigration laws, and say it's up to them to make up for inadequate federal border efforts.

"The argument that the states can't do anything to combat illegal immigration is just wrong," Maricopa County Attorney Andrew Thomas said.

His office helped draft the bill for sponsor state Sen. Russell Pearce. The legislation cleared the Senate on a 16-12 vote on June 15. 

Some local politicians "don't have the courage to stand up for their citizens," Pearce said.

Former Gov. Janet Napolitano, who is now the nation's homeland security secretary, vetoed two similar proposals in 2006, saying immigrants who sneak into the state shouldn't be made into criminals.

Under this year's proposed trespassing provision, a first offense would be a top-tier misdemeanor punishable by up to six months in jail. Subsequent violations would be a felony that could carry a penalty of up to 2 1/2 years in prison.

Agencies arresting first-time offenders would have the option of prosecuting them or turning them over to federal authorities.

Linton Joaquin, general counsel for the National Immigration Law Center, an advocacy group for low-income immigrants, said a state can play a part in immigration enforcement -- such as calling federal authorities when arresting an illegal immigrant on a state criminal violation -- but a state can't have statutes that are, in effect, immigration laws.

Opponents add that such a law would detract from officers' traditional roles in combating crimes in their communities. They say officers who aren't schooled in the complexities of immigration law would likely approach people based solely on their appearance.

Robert DeVries, president of the Arizona Association of Chiefs of Police and police chief for Kingman, a town in western Alaska, said communities better be prepared for the cost of errors made by police officers untrained in immigration law. 

"It exposes the community down the line if mistakes were to occur," said DeVries, whose group opposes the measure.

The Associated Press contributed to this report.