Newly unionized workers pressing for health benefits at a company that collects residential trash and recyclables for Montgomery County charge that the firm has retaliated by threatening them with immigration enforcement.

Fifty-seven predominantly Latino drivers and helpers for the Gaithersburg-based Potomac Disposal went on strike Monday, disrupting trash pickup for about 8,000 homes in Silver Spring and Potomac. Workers said they planned to remain off the job on Tuesday as well.

The company, one of three that Montgomery uses for trash service, has a $5 million annual contract with the county government for a total service area of about 40,000 homes.

Workers and officials for the Laborers International Union of North America said contract talks, ongoing since workers voted to unionize about six months ago, focused on their demand for employer-provided health insurance. When employees reported for work Friday morning, they found I-9 forms — required by the federal government to verify the identity of all U.S. workers — attached to their time cards.

Workers said that until Friday they had never been asked to fill out such forms.

“They’ve never made it an issue,” said Yovany Ramos, a Potomac driver for 21 / 2 years. “They’ve never harassed people until now. It’s a scare tactic.”

Company President Lee Levine could not be reached for comment Monday. A woman answering the phone at the Gaithersburg offices said, “We don’t have any comment right now.”

Brian Petruska, an attorney for the union, said the law requires employers to obtain I-9 forms from workers when they are first hired. The law does not prohibit companies from distributing them again, he said, but there had to be a legitimate reason.

Petruska said the forms were attached to time cards as workers started talking openly about how negotiations had stalled over economic issues. The strike was not triggered by contract talks but by the company implicitly threatening to place them at risk of immigration action by authorities.

“The employer provoked this by putting the I-9s on the forms. From [the workers’] point of view they know exactly what this means,” Petruska said, adding that employees would return to work immediately if the company rescinded the form.

Jhunio Medina, an organizer with the Laborers International Union, said employer attempts to use immigration laws as leverage in bargaining is a familiar tactic.

“A lot of companies do that in the hope that workers see it, get scared and back off,” Medina said.

Patrick Lacefield, spokesman for County Executive Isiah Leggett (D), said county contractors are required under the law to affirm the immigration status of workers. “I guess the question would be, did they not do that prior to this? We need to know a little more information about it.”

Potomac drivers make a daily rate of between $120 to $130 a day before taxes, or about $36,000 a year. Helpers, who ride along to empty the containers, get between $60 and $70 daily, or about $19,000 a year. The days begin at 6 a.m. with each crew responsible for trash recyclables and yard waste at anywhere from 900 to 1,300 homes.

Because the hours can vary week to week, Petruska said it is not clear whether Potomac is completely compliant with the county’s living wage law, which requires Montgomery government contractors to pay at least $13.95 an hour. But wages are not at the heart of the negotiation, workers said.

“This job is demanding, and we get hurt,” said Jacob Alvial, another driver. “The main thing we want is health care.”

Union representatives said that the company had offered health insurance to drivers, but at a cost of about 10 percent of their paychecks. Helpers were not eligible for insurance under the company proposal. The union said it offered a less expensive health plan, but one that could only be underwritten with employer contributions.

Union officials said Potomac workers feel a sense of urgency because of the requirement under the Affordable Care Act that all Americans obtain health insurance from either employers, an expanded Medicaid program or by buying it through state exchanges. Employers will not face sanctions in 2014 for failing to provide affordable insurance.

For workers hovering around the poverty line, like many of those at Potomac Disposal, paying for it themselves will be a burden no matter where it comes from.

Blanca Borcillo, a Potomac driver, said she pays Aetna $220 a month for a policy that covers her and her husband. The cost represents more than 10 percent of her monthly income.

“We want to be treated better,” she said.