Mexico's government has strongly condemned Arizona's controversial new anti-illegal-immigration law.
Mexican President Felipe Calderon says the measure will open the door to "intolerance, hate, discrimination and abuse" of Mexican citizens.
Calderon, who is making an official state visit to Washington in May, called the law "unjust" and vowed to fight it.
"My government will not stand by while political acts like this violate the human rights" of Mexican citizens, Calderon said.
The president of the Mexican Senate, Carlos Navarrete Ruiz, called the new measure "unacceptable to Mexico." Navarrete and other politicians say Mexico must send a strong message to Washington that harassment of its citizens in Arizona will not be tolerated.
The law, which both supporters and opponents are calling the toughest in the nation, requires police to question suspected illegal immigrants and orders people to carry proof of their immigration status. Arizona Gov. Jan Brewer, a Republican, signed the bill into law April 23.
Mexico is Arizona's largest trading partner. In addition to the hundreds of thousands of Mexicans who work illegally at low-wage jobs in the state, hundreds of thousands of others go to Arizona each year to shop, study or conduct business.
On Tuesday, the Mexican secretary of foreign relations issued a travel warning for Arizona. The notice tells Mexicans to take "extreme precautions" if traveling to the border state. It warns Mexican citizens that under the new law they could be subject to harassment and questioning "without cause at any moment."
The Mexican press has covered the story extensively. National TV networks have dispatched their own reporters to Arizona. The story has dominated the front pages of newspapers all week; opinion pages and cartoonists are universally denouncing the law.
Calderon says he will bring up his government's displeasure over the measure when he meets with President Obama at the White House next month.