The Biden administration will publish in the coming days a rule requiring private businesses to ensure their employees are vaccinated against Covid-19, the Department of Labor said Monday.

The rule applies to businesses with 100 or more employees. It’s estimated to cover about two-thirds of the private sector workforce.

The development comes immediately after the White House issued separate vaccine-enforcement guidelines for federal contractors that apply to millions of workers.

Companies must develop and enforce a mandatory Covid vaccination policy unless they create a plan that gives workers the option to get tested regularly and requires them to wear a mask at work, according to a Labor Department spokesperson.

The mandate will also require employers to provide paid time to workers to get vaccinated and paid sick leave to recover from any side effects.

White House officials at the Office of Management of Budget have held dozens of meetings with industry lobbyists and labor unions over the past several weeks as they reviewed the rule. The OMB completed its review on Monday and the mandate is expected to go into effect after it is published in the Federal Register.

“The Federal Register will publish the emergency temporary standard in the coming days,” a Labor Department spokesperson said Monday.

The Occupational Safety and Health Administration, which will enforce the mandate, is developing the rule under emergency authority that allows the agency to bypass the normally lengthy process to issue new workplace safety standards. OSHA can use this emergency authority if the Labor secretary determines workers face a grave danger from a new hazard.

Nearly every Republican attorney general in the country has threatened to sue the Biden administration over the mandate.

Business groups have asked the administration to delay the mandate until after the busy holiday season over concerns that workers could quit rather than follow the new rules, possibly exacerbating already tight staffing and causing supply chain disruptions. Former officials with OSHA told CNBC businesses will likely have some time to implement the rules.

The AFL-CIO, which represents the largest group of labor unions in the country, has asked the White House to include additional worker protections in the mandate, such as ensuring masks are worn in the workplace, ventilation systems are properly maintained and social distancing guidelines are followed where appropriate.

Here is the Labor Department spokesman’s full statement:

“The Occupational Safety and Health Administration has been working expeditiously to develop an emergency temporary standard that covers employers with 100 or more employees, firm- or company-wide, and provides options for compliance. Covered employers must develop, implement, and enforce a mandatory COVID-19 vaccination policy, unless they adopt a policy requiring employees to choose either to get vaccinated or to undergo regular COVID-19 testing and wear a face covering at work. The ETS also requires employers to provide paid time to workers to get vaccinated and paid sick leave to recover from any side effects. On November 1, the Office of Management and Budget completed its regulatory review of the emergency temporary standard. The Federal Register will publish the emergency temporary standard in the coming days.”