Most employers won't face a fine next year if they fail to offer workers health insurance, the Obama administration said Monday, in the latest big delay of the health-law rollout.

The Treasury Department, in regulations outlining the Affordable Care Act, said employers with 50 to 99 full-time workers won't have to comply with the law's requirement to provide insurance or pay a fee until 2016. Companies with more workers could avoid some penalties in 2015 if they showed they were offering coverage to at least 70% of full-time...