Labors International Union of North America President Terry O’Sullivan has become the latest Big Labor leader to demand that President Obama make major changes to his health care law. In a letter to the president Thursday, O’Sullivan warned that Obamacare would have “destructive consequences” for his members if key provisions were not changed.

O’Sullivan is concerned about the law’s impact on multi-employer health care plans, which are widely used by unions for their members. The plans are organized as nonprofits. Under Obamcare, they get no subsidies and are subject to penalties, raising the cost of the plans overall.

Unions fear the law will cause businesses to pull out of multi-employer plans as well as limit worker hours to offset the higher health care costs.

“Approximately 3 million laborers, retirees, and their families now face the very real prospect of losing their health benefits. This, I must remind you, was something that you promised would not happen,” O’Sullivan wrote, according to the Wall Street Journal.

This in turn will hurt labor organizing, he warned, because health care benefits are a major reason why people join unions in the first place.

O’Sullivan’s letter follows a similar one sent by the leaders of the Teamsters, the United Food and Commercial Workers Union, and Unite Here to Democratic leaders Sen. Harry Reid, D-Nev., and Rep. Nancy Pelosi, D-Calif., last week.

The United Union of Roofers, Waterproofers and Allied Workers has gone even further and called for Obamacare’s repeal.

Big Labor had been working behind the scenes to get the White House to make changes to the law, but has been rebuffed by the administration. So leaders like O’Sullivan are now making their disputes public.

Ironically, most unions had been enthusiastic proponents of Obamacare when it was being debated in Congress. LIUNA was one of the few that didn’t back the law.