A federal judge refused to block key parts of Alabama's immigration law on Wednesday, which some call the nation's toughest, including a measure that requires immigration status checks of public school students.

U.S. District Judge Sharon Blackburn, appointed by Republican President George H.W. Bush, wrote in her 115-page opinion that some parts of the law are in conflict with federal statutes, but others aren't.

She said federal law doesn't prohibit checking students or suspects pulled over by police. She also refused to stop provisions that allow police to hold suspected undocumented immigrants without bond; bar state courts from enforcing contracts involving undocumented immigrants; make it a felony for an undocumented immigrant to do business with the state; and make it a misdemeanor for an undocumented resident not to have immigration papers.

She didn't say when those and other parts of the law could take effect, but her previous order blocking enforcement expires on Thursday. Neither Gov. Robert Bentley nor Alabama Attorney General Luther Strange had any immediate comment on when the state would begin enforcing parts of the law.

Blackburn's order temporarily blocked four parts of the law until she can issue a final ruling. Those measures would:

— Make it a crime for an undocumented immigrant to solicit work.

— Make it a crime to transport or harbor an undocumented immigrant.

— Allow discrimination lawsuits against companies that dismiss legal workers while hiring undocumented immigrants.

— Forbid businesses from taking tax deductions for wages paid to workers who are in the country illegally.

Blackburn heard arguments from opponents including the Obama administration, immigrant-support groups and civil libertarians before it was supposed to take effect Sept. 1. The Justice Department contended the state law encroaches on the federal government's duty to enforce immigration law, and other opponents argued it violated basic rights to free speech and travel.

She put the entire law on hold last month, but didn't rule on whether it was constitutional, saying she needed more time.

Similar, less-restrictive laws have been passed in Arizona, Utah, Indiana and Georgia, and federal judges already have blocked all or parts of those.

Immigration became a hot issue in Alabama over the last decade as the state's Hispanic population grew by 145 percent to about 185,600. While the group still represents only about 4 percent of the population, some counties in north Alabama have large Spanish-speaking communities and schools where most of the students are Hispanic.

Alabama Republicans have long sought to clamp down on illegal immigration and passed the law earlier this year after gaining control of the Legislature for the first time since Reconstruction. GOP Gov. Robert Bentley signed it, saying it was vital to protect jobs of legal residents.

Both supporters and critics say it is the nation's toughest partly because of a section that would require public schools to verify the citizenship status of students and report statistics to the state. undocumented immigrants wouldn't be barred attending public schools, but opponents contend the law is designed to decrease enrollment by creating a climate of fear.

In a statement on behalf of 150 United Methodist pastors who signed a letter opposing the law, Revs. Matt Lacey and R.G. Lyons said church leaders were "pleased to see some of the harsh and far-reaching elements of the law have been struck down."

"We feel that many of these elements, written by members of the State House and Senate who campaign on Christianity, are not representative of the message of Christ who welcomed the stranger despite country of origin or status," they said.

Based on reporting by the Associated Press.

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