"President Biden's announcement prompts critical questions that require immediate clarification," said the Consumer Brands Association, which represents makers of packaged goods. "As with other mandates, the devil is in the details. Without additional clarification for the business community, employee anxieties and questions will multiply."

Betsy Booren, vice president of regulatory and technical affairs for the association, said packaged-goods companies now face pressing questions such as how to document compliance and how their performance will be tracked. Businesses are also dealing with "vaccine hesitancy" in the workforce, which is compounded by the fact that only the Pfizer-BioNTech shot has been fully cleared by regulators. Industry-specific guidelines from different regulators will also be key, she said.

"What I hope we'll not have is a delay of weeks and months to get some basic answers," Booren said in an interview.

Under Biden's new approach, which represents a significant hardening of the administration's position on vaccine mandates, the Occupational Safety and Health Administration will develop an emergency regulation requiring companies with 100 or more employees to require staff to be vaccinated or tested weekly, and to give paid time off to get inoculated. Employers could face fines of nearly $14,000 per violation, one official said. It is expected to take effect in the coming weeks.

Companies that don't already mandate vaccines for all employees, including General Motors Co. and Delta Air Lines Inc., issued statements detailing the efforts they've made to get employees inoculated but didn't say whether they endorse the Biden plan. Others, including Walgreens Boots Alliance Inc. and Intel Corp., are studying it.

The price tag is a concern.

"It is important that undue compliance costs do not burden manufacturers," said Jay Timmons, chief executive officer of the National Association of Manufacturers, in a statement.

In spite of the uncertainty, business groups say they support the overall effort to get workers vaccinated in order to prevent the spread of Covid-19, particularly as the more-contagious delta variant spreads and threatens to undo progress in fighting the pandemic.

Companies' responses so far this year have been largely patchwork. While they're seen as legal, vaccine requirements may still be challenged in court, raising the prospect of costly litigation. Businesses are also struggling to get enough workers, so many are reluctant to alienate those who distrust the vaccination.

More companies are starting to require the vaccine, however. Major employers including Walmart Inc., United Airlines Holdings Inc., Walt Disney Co. and Google are among those that have moved in that direction. Some, like McDonald's Corp., have mandated shots for office workers but not for frontline employees.

The mandates follow more than a year of upheaval, which started as months of lockdowns for nonessential businesses and new costs in the form of face masks, hand sanitizer and plexiglass barriers, along with the need to develop safety protocols. Now, companies are facing a new set of potentially complex requirements.

The U.S. Chamber of Commerce said it "will carefully review the details of the executive orders and associated regulations, and will work to ensure that employers have the resources, guidance, and flexibility necessary to ensure the safety of their employees and customers and comply with public health requirements."

–With assistance from Angelica LaVito, Leslie Patton, Josh Wingrove and Jillian Ward.

Read more: 

• Worker sues hospital employer: "Taking the vaccine will offend and otherwise harm the Holy Spirit"
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• Virus surge upends plans for getting workers back to offices

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