US teachers unions and Hispanic activists said Wednesday that an Arizona-style immigration law upheld by a federal judge last week is creating a "humanitarian crisis" as thousands of parents keep their children home, fearing that teachers will act as immigration agents.

Alabama's first Republican supermajority since Reconstruction approved this summer what many consider America's toughest immigration law. And last week, federal Judge Sharon Lovelace Blackburn surprised many Americans when she upheld key parts of the law – including a portion that says schools must check the immigration status of children when they enroll, as well as the status of their parents.

"This law revisits Alabama's painful racial past," Sam Brooke, a staff attorney for the Southern Poverty Law Center in Montgomery, Ala., said in a conference call with reporters Wednesday. "When a law that demonizes people to the point of pushing children out of schools is cheered, it's a dark day for the state and the country."

Lawmakers and Gov. Robert Bentley (R) have said they were forced to pass the state law because the US government had failed to enforce federal immigration statutes. The state law is designed to ensure the safety and economic security of Alabamians, the officials say.

”It’s heartbreaking to read about [children being pulled out of school], but it’s going to be an immigration bill or it’s not going to be one," state Sen. Rusty Glover (R) told the American Independent News Network. Senator Glover voted for the law and is a history teacher in Semmes.

Federal courts have struck down large parts of similar legislative attempts by other states, but Judge Blackburn allowed key provisions in the Alabama law to stand, saying they passed constitutional muster because they reinforced existing federal law.

Teachers unions and Hispanic advocacy groups, as well as the Obama administration, have filed an appeal, but the law began to take effect this week. Some 2,000 Hispanic students did not show up to school Monday, according to state education officials. That figure amounts to about 7 percent of the state's Hispanic student population.

Yet education officials have vowed that even children without birth certificates attempting to enroll will be allowed to attend school. Information about a child’s immigration status "will not be used to individually identify your child," but rather will be used only to report "statistical data," interim state superintendent Larry Craven said in a statement Wednesday.

The statistics will be gathered by the state Department of Education to track the cost of educating illegal immigrants.

The US Supreme Court ruled in 1982 that states cannot deny a free public education to undocumented immigrants. Hispanic advocates said they've been counseling parents to send their children to school.

Still, Hispanics – many of them part of families where the children are US citizens, but the parents are illegal immigrants – are responding to "a fear factor out there that's written between the lines of this law,” said Roseann Rodriguez of the Hispanic Interest Coalition of Alabama, which is one of the plaintiffs in the case. Such a fear factor “is accomplishing the impact of folks who want to see these families leave," said Ms. Rodriguez during the Wednesday conference call.

The big question is whether the students absent this week will return once, and if, fears about being reported to immigration authorities fade.

American Federation of Teachers president Randi Weingarten said Alabama has crossed an unprecedented line, waging a political battle over immigration on the backs of children.

"Parents are afraid to drive their kids to school, [fearing] that something will happen and they won't be able to care for their children," she said. "Nobody wins when a law pushes children into the shadow of society. Teachers should be safety nets, not snitches. Guardians, not guards."