"Mexico has an interest in protecting its citizens and ensuring that their ethnicity is not used as basis for state-sanctioned acts of bias and discrimination," the brief said, according to the paper.

A 16-nation brief is different from a lawsuit and in many respects is symbolic without much legal weight.

Argentina, Boliva, Brazil and Colombia among other Central and South American countries are also named on the brief.
If Mexico, and the 15 other countries suing Alabama were really concerned about their citizens being treated fairly, government officials in those countries would take steps to improve their citizens' situation at home so they don't have to come to America for economic opportunity. Mexico specifically has vast natural resources including oil, gas and gold, yet the government has not created the economic environment for people to create jobs and prosper in the country.
Also, hypocrisy comes into play here considering Mexico has much harsher immigration laws than the United States. The Washington Times pointed this out back when Arizona's SB 1070 was signed in 2010.
Mexican President Felipe Calderon denounced as “racial discrimination” an Arizona law giving state and local police the authority to arrest suspected illegal immigrants and vowed to use all means at his disposal to defend Mexican nationals against a law he called a “violation of human rights.”

But the legislation, signed April 23 by Arizona Gov. Jan Brewer, is similar to Reglamento de la Ley General de Poblacion — the General Law on Population enacted in Mexico in April 2000, which mandates that federal, local and municipal police cooperate with federal immigration authorities in that country in the arrests of illegal immigrants.

Under the Mexican law, illegal immigration is a felony, punishable by up to two years in prison. Immigrants who are deported and attempt to re-enter can be imprisoned for 10 years. Visa violators can be sentenced to six-year terms. Mexicans who help illegal immigrants are considered criminals.

The law also says Mexico can deport foreigners who are deemed detrimental to “economic or national interests,” violate Mexican law, are not “physically or mentally healthy” or lack the “necessary funds for their sustenance” and for their dependents.

“This sounds like the kind of law that a rational nation would have to protect itself against illegal immigrants — that would stop and punish the very people who are violating the law,” said Rep. Steve King of Iowa, ranking Republican on the House Judiciary subcommittee on immigration, citizenship, refugees, border security and international law.

“Why would Mr. Calderon have any objections to an Arizona law that is less draconian than his own, one he has pledged to enforce?” Mr. King said.

Sen. Jon Kyl of Arizona, the ranking Republican on the Senate Judiciary subcommittee on terrorism and homeland security, described Mr. Calderon’s comments as “hypocritical to say the least.”