Big Labor officials are negotiating with Obama administration officials on a "fix" to spare multi-employer pension plans, which are provided by many unions to their members, from the higher costs they would face under the president's health care law.

A forthcoming report estimates the cost to taxpayers for that fix at $187 billion over 10 years.

Multi-employer plans — also known as "Taft-Hartley" plans — are ineligible for federal subsidies under Obamacare. This has many unions worried, since it will raise the cost of the plans, pushing employers to either limit coverage or pull out altogether. Some are already moving in that direction

Labor leaders have furiously lobbied Obama and congressional leaders to extend subsidies to the plans, but — so far — the administration has not moved.

A study by American Action Forum, a nonprofit think tank founded by Douglas Holtz-Eakin, former Congressional Budget Office director, suggests why: It will cause Obamacare's costs to skyrocket at a time when the administration is already struggling to keep them under control.

The report obtained by the Washington Examiner, found: "If subsidies were extended to union workers and their families enrolled in Taft-Hartley plans, it would bring 3 million more households onto the rolls and cost an additional $16 billion in 2014 alone. Beyond that if the number of union members in Taft-Hartley plans remains constant (it would likely increase), this estimate grows to $187 billion within the first 10 years."

UPDATE: The full AAF study can be found here.