They've been threatening to do it for weeks so it's no big surprise - except perhaps the timing.

Huge majorities like the AZ immigration law and it's a safe bet that the White House waited until the issue cooled off before dumping this news on a Friday afternoon:

The confirmation comes after Secretary of State Hillary Clinton said in an interview with a TV station in Ecuador earlier this month that the administration would challenge the law in court, though officials had long said the issue was under review.

Administration officials initially would not confirm Clinton's statement. But an official told Fox News on Friday that while the review is still underway, the decision has already been made that a Department of Justice suit will be filed. The administration at this point is just building its case.

Another official said there are still "substantial" issues to address and work out before the Justice Department knows that it has a strong enough case to file a lawsuit. The official said the department intends to file suit, but that any court action is contingent on the final review.

Clinton's announcement was met with outrage Thursday by Arizona Gov. Jan Brewer, who signed the law. Brewer told Fox News she's ready for a fight.

"What a disappointment," Brewer told Fox News' Greta Van Susteren on Thursday, saying she was shocked the administration would make such an announcement on foreign TV without giving Arizona officials the news first.

Brewer is being a little disingenuous. To be shocked by anything this administration does is to have been asleep for a year and a half. They're not telling the governors of Louisiana and Alabama how much of their coastline is affected by the oil spill so why should they tell Brewer they're about to haul her into court?

I'm afraid the Supreme Court has a history of siding with the feds in battles like this so it is more than likely that AZ will lose. But as a shot across the bow to the federal government, not to mention a potent campaign issue, Arizona has already given us a great victory.