Disputes between unions and employers over paying for new costs associated with the Affordable Care Act are roiling labor talks nationwide.

Unions and employers are tussling over who will pick up the tab for new mandates, such as coverage for dependent children to age 26, as well as future costs, such as a tax on premium health plans starting in 2018. The question is poised to become a significant point of tension as tens of thousands of labor contracts covering millions of workers expire in the next several years, with ACA-related cost increases ranging from 5% to 12.5% in current talks.

In Philadelphia, disagreement over how much workers should contribute to such health-plan cost increases has stalled talks between the region's transit system and its main union representing 5,000 workers as they try to renegotiate a contract that expired in March.

Roughly 2,000 housekeepers, waiters and others at nine of 10 downtown Las Vegas casinos voted this month to go on strike June 1 if they don't reach agreements on a series of issues, the thorniest of which involve new ACA-related cost increases, according to the union.