President Joe Biden on Thursday announced new federal vaccine requirements affecting as many as 100 million Americans in the most expansive effort by the administration to increase COVID-19 vaccinations and curb the surging Delta variant.

Addressing the nation from the White House, Biden pointedly criticized the "unvaccinated minority"', roughly 80 million Americans he said who haven't been vaccinated despite months of availability and incentives.

"We've been patient. But our patience is wearing thin, and your refusal has cost all of us," he said. The unvaccinated minority "can cause a lot of damage, and they are".

Biden said "we're going to reduce the spread of COVID-19 by increasing the share of the workforce that is vaccinated in businesses all across America.

"We are in the tough stretch, and it could last for a while," Biden said of the current state of the pandemic. "We can and we will turn the tide on COVID-19."

Biden announced the new requirements as polls show doubts among the public over his handling of the pandemic.

A new rule announced by Biden will mandate that all employers who have more than 100 workers must require them to be vaccinated or test for the virus weekly, affecting about 80 million Americans. The rule also would require that large companies provide paid time off for vaccination. The White House didn't immediately say when it would take effect but said workers would have sufficient time to get vaccinated.

Biden's announcement generated stern opposition from Republicans online, with a common thread questioning the constitutionality of the mandates.

"My legal team is standing by ready to file our lawsuit the minute @joebiden files his unconstitutional rule," South Carolina Governor Kristi Noem wrote on Twitter. "This gross example of federal intrusion will not stand."

"The US Constitution does not give the president this type of authority," said Representative Robert Aderholt of Alabama. "Nowhere in Article 2 of the Constitution will you find anything that even remotely gives the president this kind of power."

Roughly 17 million workers at healthcare facilities that receive federal Medicare or Medicaid also will have to be fully vaccinated. The Centers for Medicare and Medicaid Services will extend a vaccination requirement issued earlier this summer — for nursing home staff — to other healthcare settings including hospitals, home-health agencies and dialysis centers.

Biden said he is also signing an executive order to require vaccination for employees of the executive branch and contractors who do business with the federal government, with no option to test out. That covers several million more workers.

He also announced a doubling of federal fines for airline passengers who refuse to wear masks on flights or to maintain face-covering requirements on federal property in accordance with Centers for Disease Control and Prevention (CDC) guidelines.

He said the federal government will work to increase the supply of virus tests and that the White House has secured concessions from some retailers to sell at-home testing kits at cost beginning this week.

Biden's order for executive branch workers and contractors includes exceptions for workers seeking religious or medical exemptions from vaccination. Federal workers and contractors will have 75 days to get fully vaccinated. Workers who don't comply will be referred to their agencies' human resources departments for counseling and discipline, to include potential termination.

Biden's measures should help, but what's really needed is a change in mindset for many people, said Dr Joshua Sharfstein, vice-dean at the Johns Hopkins Bloomberg School of Public Health in Baltimore.

"There is an aspect to this now that has to do with our country being so divided," he told The Associated Press. "This has become so politicized that people can't see the value of a vaccination that can save their lives. Our own divisions are preventing us from ending a pandemic."

Representative Greg Murphy, a North Carolina Republican and practicing physician, told Fox News: "As I have repeatedly said, the decision about whether or not to take the COVID-19 vaccine, like every other medical decision, is one that should be made between a patient and a doctor."

An AP-NORC poll conducted in August found 55 percent of Americans in favor of requiring government workers to be fully vaccinated, compared with 21 percent opposed. Similar majorities also backed vaccine mandates for healthcare workers, teachers working at K-12 schools and workers who interact with the public, as at restaurants and stores.