The ruling comes after four days of testimony that included Bill Garrett, the senior vice president of operations at McDonald's, and two days after another judge in California granted a temporary restraining order against a McDonald's franchise in a case in which employees at a store were told to wear coffee filters and doggie diapers as masks.

"The preliminary injunction shows that McDonald's restaurants failed to keep their workers safe amid the COVID-19 pandemic and posed a danger to public health, particularly when it came to social distancing and masks," Danny Rosenthal of James & Hoffman in Washington, D.C., an attorney for the plaintiffs, wrote in an emailed statement.

"We are pleased that Judge Reilly issued an injunction that will not only help keep workers safe, but will also protect workers' families, McDonald's customers, and the community at large," Rosenthal said.

McDonald's, represented by Jonathan Bunge of Quinn, Emanuel, Urquhart & Sullivan, said in an emailed statement that the judge found its COVID-19 policies did many things right.

"McDonald's is pleased the judge found that strong measures are already in place across these Chicagoland restaurants to create a safe experience for customers and crew, including providing sufficient supply of masks, gloves and sanitizers and sufficiently monitoring for COVID cases, as McDonald's is doing throughout the country," the statement said.

"These measures are part of the 50 processes we have enhanced during the pandemic to keep restaurant employees and customers safe. We have also issued a 59-page guide outlining national minimum restaurant standards, including adhering to social distancing guidelines for customers and crew, conducting wellness and temperature checks, requiring protective barriers, face masks and gloves, increasing the frequency of handwashing and providing contactless purchasing options to customers."

The case, filed on May 19, involved five employees at four McDonald's locations in Chicago, and four people who lived with them, alleging the restaurant chain had failed to provide enough protections from the coronavirus. The case is one of the few to ask a judge to order a business to impose COVID-19 protections, the most prominent of which involved a public nuisance case against meat processor Smithfield Foods Inc. that ended in an order denying the plaintiffs' injunction request.

McDonald's also faces another class action, brought on June 16, alleging the restaurant chain created a public nuisance at a store in Oakland, California, by allowing 23 people to get sick with COVID-19, including a 10-month-old baby.

The class action in Chicago alleges both public nuisance and negligence claims against McDonald's and two franchise owners, one of which dropped out of the case after selling its store. Two of the stores had COVID-19 cases among their employees, according to the judge's order.

McDonald's lost an attempt to dismiss the case on jurisdictional grounds, setting the stage for a showdown over a potential preliminary injunction.

In addition to Garrett, the preliminary injunction hearing, held via Zoom and broadcast live on YouTube, featured lengthy testimony from the plaintiffs, store managers and experts on both sides, and numerous slides of store signs, layouts and photographs.

In her ruling, Reilly found that McDonald's had provided much of what the plaintiffs initially had asked for, such as hand sanitizer and masks. She also found that its policies, such as posting signs requiring customers to wear masks and installing Plexiglas at the counter and drive-thru, were "not unreasonable."

But, she noted, McDonald's also told employees they could be closer than six feet if they passed each other momentarily, as long as it's not for 10 minutes or more.

"McDonald's has created an environment that leads employees, including managers, to believe they can take off their masks and stand within 6 feet of each other as long as they do not do so in excess of 10 minutes," Reilly wrote. "This increases the health risk for the employees, their families and the public as a whole and conflicts with the governor's order on social distancing potentially undoing any good it has done as we fight this incredibly contagious disease."

She also cited photographic evidence and the testimony of employees that workers stood within six feet of each other without properly wearing masks—both of which were "serious failures." Social distancing and masks, she wrote, were key elements of the governor's order, as well has health guidelines from the Illinois Department of Public Health and the U.S. Centers for Disease Control and Prevention.

"Although neither in and of themselves necessarily create a substantial or unreasonable interference with the public's or the plaintiffs' rights, the combination certainly does," she wrote.

She denied an injunction as to the plaintiffs' negligence claims, calling their alleged injuries "speculative" given that none of the plaintiffs had evidence of COVID-19 exposure or infection.