BATH — A fourth Bath Iron Works employee tested positive for coronavirus, the company announced Thursday, amid a union strike at the shipyard.

The employee was last at work on June 18, according to a statement from the company, but details such as the worker’s name and where they worked in the shipyard were not released.

The company said it notified employees who came in close contact with the worker and is “continuing to urge any employees with symptoms consistent with COVID-19 or who have been in contact with someone who has tested positive to self-report to BIW management. In addition, we are urging all employees to adhere to CDC guidance on social distancing and the use of facial coverings to reduce the spread of the virus from person to person.”

The first case at the shipyard was in late March. Another positive case followed in early April, and the third case was announced earlier this month. Those three workers recovered and returned to work, according to a statement from the company.

In March and April, as the number of cases in Maine steadily rose, union officials and Maine lawmakers called on the company to close to prevent the virus from spreading within the shipyard, which employs 6,700 people from every county in the state. The shipyard stayed open, but ramped up cleaning and encouraged employees to start wearing masks or face shields when close to other workers.

“At Bath Iron Works, the safety of our employees continues to be our top priority, and we are committed to supporting them as we navigate these unprecedented times as an industry essential to the defense of our nation,” the company said.

The company said employee attendance plummeted after that initial test, with only 41 percent of workers clocking in two days after the shipyard announced the first positive test.

This week, fewer than half of the shipyard’s employees are clocking in as the company’s largest union continues to strike for changes to its new contract. However, nearly all picketers have decided against wearing a face mask while picketing, though the CDC recommends masks in public because the virus is believed to spread through respiratory droplets.

The Maine Center for Disease Control & Prevention has recorded 3,070 cases since mid-March — 2,731 confirmed cases and 339 probable cases. Of those, 2,512 people have recovered and 103 people have died, leaving 455 active cases, 31 more than Wednesday, the Portland Press Herald reported.