ObamaCare still needs changes since it contains “inadvertent holes,” AFL-CIO President Richard Trumka told reporters Thursday.
"When the act was put together, it wasn't thought completely through,” he said.
Several unions have expressed outrage in recent weeks over how the law would affect their members.
When the White House brushed off their complaints, they turned to Congress.
The leaders of three large unions sent a scathing letter to Senate Majority Leader Harry Reid (D-Nev.) and House Democratic Leader Nancy Pelosi of California.
"Time is running out,” they warned."Congress wrote this law. We voted for you. We have a problem -- you need to fix it."
While Trumka was critical in his comments Thursday, he indicated the administration and Secretary of Labor Tom Perez were trying to change the law to help the unions.
"He's being helpful right now," Trumka said. "He's in the middle of the talkon health care and his help on solving the problems we have on health care is very, very important and very instrumental."
But analysts wonder how the administration could make changes.
"The unions are furious,” said John Goodman of the National Center for Policy Analysis in Dallas.
"The White House is saying 'we want to do something for you.' But let me tell you, the Constitution requires the president to faithfully carry out the laws of the land, and it does not empower the president to rewrite the laws that Congress has passed."
One key union complaint is that defining part-time work as less than 30 hours encourages employers to cut workers to 29 1/2 hours to avoid the requirement to provide health insurance.
That, the unions wrote to Congress, will "destroy the foundation of the 40-hour work week that is the backbone of the American middle class."
"I mean that is something that no one intended,” Trumka said."Is that an issue? Yeah."
Meanwhile, critics note that the unions were instrumental in passing the law they now want to change.
Jim Capretta of the American Enterprise Institute says "You know, it's the height of irony that three and a half years later, the major unions around the country are all starting to say this bill is a huge problem for us."
Trumka also had some advice and a warning for politicians: listen to people's complaints about the law, and try to fix them, he said, instead of just talking about how good the law is.