Employers who hire illegal immigrants can be fined, but the Obama administration warned this week that they also can be fined for asking legal immigrants to show their green cards before hiring them.

The Justice Department's civil rights division sued the Maricopa County Community Colleges in Arizona, seeking damages from schools for having "intentionally committed document abuse discrimination."

Prior to this year, the local colleges in the Phoenix area asked job applicants who were not U.S. citizens to show a driver's license, a Social Security card and their permanent resident card, commonly called a green card.

The Justice Department said a valid driver's license and a Social Security card are usually sufficient to show that a person is authorized to work. Requesting a green card amounts to "immigration-related employment discrimination," said Thomas E. Perez, the assistant attorney general for civil rights.

Federal law forbids treating "authorized workers differently during the hiring process based on their citizenship status," Perez said. He said the department's Office of Special Counsel would bring legal actions against employers who impose "unnecessary and discriminatory hurdles to employment for work-authorized noncitizens."

Amid the fierce controversy over immigration, the Obama administration has launched three lawsuits this summer to protect the rights of Latinos and legal immigrants - all three targeting Arizona.

In July, the administration successfully blocked Arizona's law that authorized state and local police to check the immigration status of persons who were arrested. On Thursday, it sued Maricopa County Sheriff Joe Arpaio seeking documents that could show he has illegally targeted Latinos in the course of his immigration sweeps.

The suit against the Maricopa community colleges, announced Monday, and could affect employers across the nation.

"Employers are getting very mixed messages from the government," said Jessica Vaughan, a policy analyst with the Center for Immigration Studies.

On one hand, employers have been told they need to do more to verify that their workers are legal and authorized to work in the United States. Federal immigration law says hiring "an unauthorized alien" can result in fines of up to $3,000 per worker. However, another provision of the same law bars employers from requesting "more or different documents" than are needed to prove a noncitizen's legal status.

In the Maricopa college case, the Justice Department said it wanted "full remedial relief" for 247 noncitizens who applied for jobs with the community college district between August 2008 and January of this year, plus a civil penalty of $1,100 for each of them.

"We are extremely disappointed by the Justice Department's action. We had no intent to discriminate against any foreign national, and we feel we have been singled out for the maximum penalty under the law," said Charles Reinebold, a spokesman for the community colleges. "There was no actual harm here. This was a paperwork error, and we revised it after it was brought to our attention."

Vaughan said she was "very surprised the administration would resort to a lawsuit. In the past, the emphasis has been on mediation to resolve these issues."

But others applauded the administration's move to enforce the anti-discrimination parts of the immigration law.

Gening Liao, a lawyer for the National Immigration Law Center in Los Angeles, said the law itself is clear.

"If you bring in a driver's license and a Social Security card, those documents are sufficient. Employers are prohibited from asking for extra documents or different documents," she said. "This is blatant discrimination, and we get calls about it all the time. We hope to see more lawsuits like this."