Across the country, employers in many other kinds of businesses are devising strategies to comply with or, in some cases, sidestep a new requirement to provide insurance for those who work 30 hours or more. Some are breaking their businesses into smaller companies, for instance, or even laying off workers. Some companies plan to shift workers to part-time status.

But in the vast, fertile fields of California’s Central Valley, part-time labor is not realistic. Pruning, picking and packing produce is full-time, nearly year-round work.

“You can’t put your ag workers on a 28-hour workweek like Starbucks, Denny’s and Walmart are considering,” Mr. McClements said.

In places like Huron, a Central Valley town surrounded by thousands of acres of farmland, there are other, practical concerns.

On a recent morning, Jose Romero pulled weeds from a row of lush tomato plants. Mr. Romero, 36, arrived at the field around 5 a.m. and worked until sunset. Like many of the other workers in the tomato field, he was surprised to learn that his employer, Mr. Herrin at Sunrise Farm Labor, would have to offer him health coverage, and that he could be asked to contribute up to 9.5 percent of his wages to cover the costs.

“We eat, we pay rent and no more,” Mr. Romero said in Spanish. “The salary that they give you here, to pay insurance for the family, it wouldn’t be enough.”