A proposed tax on medical device manufacturers could be $10 billion more than previously planned, as lawmakers in the U.S. Senate strive to offset reductions to the tax on high-end healthcare plans demanded by labor unions.

Union contracts would be exempt from a tax on so-called "Cadillac" plans until 2018, according to the terms of a deal hammered out between the trade groups and Democratic legislators, the Wall Street Journal reported.

That means finding new revenue to pay for healthcare reform, as the healthcare plan tax will raise about $90 billion over 10 years, down from $149 billion in the Senate bill, according to the newspaper. Non-union workers would begin paying the tax in 2013.

The tax on device makers would jump to $30 billion over 10 years starting in 2011, but "wasn’t a done deal as the House was showing resistance," the Journal reported. Pharmaceutical companies and nursing home operators would also see their share of the tab rise.