Feb. 10 (Bloomberg) — Employers with fewer than 100 workers won't have to provide health insurance until 2016 under Obamacare, as the administration said it would again delay a key requirement of the health law.

Larger firms have to cover at least 70 percent of the workforce starting next year, the Internal Revenue Service said in a rule issued today.

The Patient Protection and Affordable Care Act envisioned as a cornerstone of its expansion of U.S. insurance coverage that employers with 50 or more workers would be required to provide health benefits to their employees. Under pressure from business groups, the Obama administration has weakened that requirement since July, first by delaying enforcement of the mandate until 2015. Many firms will have even more time under the regulation issued today.