* Judge would be second to rule law unconstitutional
* Ruling marks major challenge to federal authority
* Judge may seek to invalidate law, order injunction
By Tom Brown
MIAMI, Jan 31 (Reuters) - A Florida judge could on Monday become the second U.S. judge to declare President Barack Obama's healthcare reform law unconstitutional, in the biggest legal challenge yet to federal authority to enact the law.
The judge, Roger Vinson of the U.S. District Court in Pensacola, Florida, was expected to rule on a lawsuit brought by governors and attorneys general from 26 U.S. states, almost all of whom are Republicans. Obama is a Democrat.
The plaintiffs represent more than half the U.S. states, so the Pensacola case has more prominence than some two dozen lawsuits filed in federal courts over the healthcare law.
No specific time has been given for Vinson's ruling, which was unlikely to end the legal wrangling over the contentious reform law, which could well reach the U.S. Supreme Court.
But an aide said he was determined to issue his opinion in the course of Monday on the suit filed on March 23, 2010, just hours after Obama signed the reform into law.
The healthcare overhaul, a cornerstone of Obama's presidency, aims to expand health insurance to cover millions of uninsured Americans while also curbing costs. Administration officials insist it is constitutional and needed to stem huge projected increases in healthcare costs.
Two other district court judges have rejected challenges to the "individual mandate," the law's requirement that Americans start buying health insurance in 2014 or pay a penalty.
But a federal district judge in Richmond, Virginia, last month struck down that central provision of the law in a case in that state, saying it invited an "unbridled exercise of federal police powers."
The provision is key to the law's mission of covering more than 30 million uninsured. Officials argue it is only by requiring healthy people to purchase policies that they can help pay for reforms, including a mandate that individuals with pre-existing medical conditions cannot be refused coverage.
'WITHOUT PRIOR PRECEDENT'
Vinson has suggested strongly that he too will rule the individual mandate oversteps constitutional limits on federal authority. He may also move to invalidate the entire law, by granting the plaintiff states' request for an injunction to halt its implementation.
"The power that the individual mandate seeks to harness is simply without prior precedent," Vinson wrote in an earlier opinion in October.