* AFL-CIO says White House decision is "troubling"
* Business groups remain concerned about employer mandate
* Republicans want to know why they weren't informed sooner (Adds reaction, details)
By Caren Bohan and Yasmeen Abutaleb
WASHINGTON, July 3 (Reuters) - Republicans launched a fresh assault on "Obamacare" Wednesday, promising a congressional inquiry after the White House delayed a requirement for employer-provided health insurance until after the 2014 congressional elections.
Meanwhile, the AFL-CIO labor organization, which supports the health care law, asked that its own requests for changes be given the same consideration the White House has extended to employers.
That raises the prospect of numerous interest groups seeking to reopen previously settled disputes over the 2010 law.
The criticisms complicate White House efforts to boost public support for President Barack Obama's signature domestic policy achievement. The law's success depends in part on convincing millions of Americans to sign up for coverage.
The requirement that employers with 50 or more workers provide health coverage was set to begin at the start of 2014. Now the mandate will not begin until 2015.
The White House has said the delay for employers will not affect or delay the health exchanges that Americans will use to buy insurance.
"This is a demonstration of our willingness to work with the business community," said White House Deputy Press Secretary Josh Earnest, arguing that the delay should "inspire confidence" for that reason.
But a committee of the Republican-controlled House of Representatives wrote administration officials, including Treasury Secretary Jack Lew, asking why lawmakers were not informed sooner that the administration was considering delaying the requirement for employer-provided health insurance.
"Despite delays and missed deadlines, administration officials had repeatedly testified before Congress that they were still on schedule to implement the law," said Representative Fred Upton, chairman of the House Energy and Commerce Committee.
Whether or not an investigation promised by Upton's committee sheds light on the decision, it promises to prolong negative publicity about the law less than six months before it is to be rolled out.
In postponing the employer mandate on Tuesday, Upton said in a statement, the administration "admitted that wasn't the case, and it's clear we have no idea the full scope of delays and disarray that may be coming."
Senator John Barrasso, a Wyoming Republican and leading critic of the health law, accused the administration of carrying out a "cynical ploy" with postponement of the employer mandate.
"The public already lacks confidence in the law and it seems that now the administration is finally admitting that this law is unworkable, unaffordable and continues to be very unpopular," Barrasso said.
Among Obama's supporters, the AFL-CIO, a staunch ally of the Democratic president, said it found the decision to postpone employer-provided coverage "troubling."
AFL-CIO President Richard Trumka complained that while the White House showed willingness to provide flexibility for the business community, it appeared reluctant to make changes sought by labor.
He said he would press his concerns and hoped the administration would address them, "just as they have the concerns voiced by employers."
Business groups said they welcomed the postponement but remained concerned about the employer mandate.
The U.S. Chamber of Commerce said the delay would help avoid "serious near-term economic consequences of the health law," but it wanted to work with the administration to head off other potential problems.
The National Association of Manufacturers said in a blog post that the employer mandate was a bad idea from the start and the administration's move "simply delays the inevitable."
The delay complicates White House efforts to make the rollout of the health law look smooth, an already challenging task in part thanks to the continuing Republican campaign to discredit the program.
Jim Manley, a former aide to Democratic Senate Majority Leader Harry Reid, said he was worried that the delay would give Republicans "another club to beat Democrats upside the head."
"There's no denying that this is a setback for the program. The perception is pretty bad," said Manley, who was involved in the effort to pass the law.
Several lawmakers, including some Democrats, had pressed the White House to consider a delay in the employer mandate. Among them was Senator Mark Begich, a Democrat in the Republican-leaning state of Alaska, who met with the White House last week to express his concerns about the law's implementation.
Begich has also written to top administration officials complaining that small businesses were overwhelmed and confused by complex information strewn across nearly 50 government websites. (Additional reporting by Steve Holland and Roberta Rampton Editing by Fred Barbash and Xavier Briand)