With a baby on the way, that paycheck was even more precious.

“Now more than ever, I need to work,” she said.

But when Ms. Valencia told her supervisors in July that she had a high-risk pregnancy, they told her she could work only without restrictions, she said. After taking time off to try to negotiate an accommodation with the company, she returned when her co-workers volunteered to handle the heavy machinery and lifting.

In August, she said, her supervisors insisted that she work overtime. Ms. Valencia felt so ill after two lengthy shifts that she went to the hospital and then to her doctor, who gave her the letter that she handed to her boss.

The response from the company came at about 9:30 a.m., when she was handed a letter written by Bob Ferla, the operations manager.

“Unfortunately, we as a company are not able to allow you to continue work,” wrote Mr. Ferla, who warned that her high-risk pregnancy could put her “at risk” in a work environment that was fast-paced, was very physical and involved machinery.

“Please understand we need a ‘full-duty release’ from the doctor,” he added, if she wanted to continue to work.

Ms. Valencia said she begged her managers to excuse her from overtime as her doctor had recommended. She pointed out that the company’s busy season typically ended in September, and that overtime was rarely needed during the rest of the year.