PHOENIX - Arizona's new immigration law will face two of its strongest challengers in federal court today in a pair of hearings that will determine whether the law takes effect on July 29, as scheduled.

U.S. District Judge Susan Bolton will first consider complaints by three civil-rights organizations that there are sufficient legal questions about the entire law to keep it from being enforced. This afternoon, the U.S. Department of Justice will make its case that half the new law is pre-empted by federal statutes.

While there is some overlap between the two cases, they have distinctly different philosophies.

The American Civil Liberties Union, the Mexican American Legal Defense and Educational Fund, and the National Immigration Law Center focus primarily on how the law would be enforced. Among the arguments is there is too much leeway in how it should be enforced to make it fair. Courts generally have said laws need to be clear about what actions will get people in legal trouble.

The argument by the Department of Justice is more straightforward: The interests of the federal government in how immigration laws are enforced automatically trumps what Arizona is trying to do.

In both cases, the defense by John Bouma, the private attorney hired by Gov. Jan Brewer, is likely to be pretty much the same: There's nothing in the state statute that conflicts with federal law, states have certain rights to enforce federal laws, and any claims of racial profiling or unfair enforcement are premature at best. In earlier, related hearings, the judge already has indicated that she is interested in the views of the federal government.

During a hearing last week on a separate request for an injunction, attorney Stephen Montoya said his client, Phoenix police Officer David Salgado, believes the law is illegal, in part because it infringes on the exclusive right of the federal government to control immigration policy. As a result, Montoya said Salgado will refuse to enforce the law, potentially putting his job with the Phoenix Police Department at risk.

Bouma said that's only Salgado's opinion.

Then, when Judge Bolton asked whether the fact the United States government is making the same argument bolsters Salgado's claim, Bouma said the decision by the Department of Justice to sue doesn't mean it is correct.

Sen. Russell Pearce, R-Mesa, who crafted SB 1070, and Gov. Jan Brewer, who signed it, said the law is necessary because of the failure of the federal government to secure the border.

The measure says its purpose is to "make attrition through enforcement the public policy of all state and local government agencies in Arizona" and to "discourage and deter the unlawful entry and presence of aliens and economic activity by persons unlawfully present in the United States."

Federal attorneys seized on that language to argue that the Arizona law is in direct conflict with the federal statute.

"By pursuing attrition and ignoring every other objective embodied in the federal immigration system … SB 1070 conflicts with and otherwise stands as an obstacle to Congress' demand that federal immigration policy accommodate the competing interests of immigration control, national security, public safety, humanitarian concerns and foreign relations," the federal lawyers argue.

The ACLU lawsuit is more focused on specific details of the law and why the judge should declare it unenforceable.

For example, one section makes it a state crime for anyone not in this country legally to "solicit work in a public place." The attorneys say it doesn't define "work," covering "innocuous activities" like an artist painting portraits in a public park and students conducting a car wash.

Find the lawsuits, court filings at