Day labourers face arrest for soliciting work if they are in the US illegally
The president of Mexico has condemned Arizona's new immigration law, describing it as discriminatory.
The legislation will require Arizona police to question people about their immigration status if they suspect they are there illegally.
Mexican President Felipe Calderon warned that relations with the US border state would suffer as a result.
Mr Calderon said he would use all means at his disposal to defend the rights of Mexican nationals.
Under the new law, day labourers face arrest for soliciting work if they are in the US illegally, and police departments can be sued if they fail to enforce the law.
Mr Calderon said on Monday that he had told Mexico's foreign relations department to intensify efforts to protect the rights of Mexicans living in the US.
He also urged the government to seek help from lawyers and immigration experts.
"Criminalising immigration, which is a social and economic phenomena, this way opens the door to intolerance, hate, and discrimination," Mr Calderon told a meeting of Mexican immigrant groups.
The BBC's Julian Miglierini in Mexico City said the new immigration law had been widely criticised in Mexico.
He said that Mr Calderon had promised his government would challenge the law using all available means, and that he would discuss the issue with US President Barack Obama in Washington next month.
The legislation was also attacked by the head of the Organisation of American States, Jose Miguel Insulza.
"We consider the bill clearly discriminatory against immigrants, and especially against immigrants from Latin America," he told the Associated Press news agency.
24 May: This is a corrected version of the story making it clear that President Calderon said he would use all means at his disposal to defend the rights of Mexican nationals.