Under the House measure, employers with payrolls exceeding $400,000 a year would have to provide health insurance or pay the 8% penalty. Employers with payrolls between $250,000 and $400,000 a year would pay a smaller penalty, and those less than $250,000 would be exempt. Certain small firms would get tax credits to help buy coverage.

The relatively low thresholds for penalties triggered the sharpest criticism yet from employer groups, who said the burden on small business is too high and doesn’t do enough to help them expand insurance coverage.

“This bill costs too much, it covers too few and it has way too much government involvement,” said Michelle Dimarob, a lobbyist with the National Federation of Independent Business, the main trade group for small firms. “Small business doesn’t want any of those things.”