People in certain jobs have become increasingly subject to vaccine requirements.

They are demonstrating against Covid-related restrictions, particularly a recent vaccination requirement for truck drivers crossing the long US-Canada border.

It says compulsory vaccines should be applicable 'only when all other feasible options to improve vaccination uptake have been exhausted'.

While it could take weeks to prove how infectious and resistant to current vaccines Omicron is, many countries have rushed to ramp up existing programmes.

The administration cites a long history of such requirements going back to George Washington requiring his troops to be inoculated against smallpox.

Petitioners include five strongly Republican US states – Texas, Louisiana, South Carolina, Utah and Mississippi – as well as several private companies and religious groups.

They say it is unconstitutional and violates federal procurement law.

This sets him up for a clash with President Joe Biden who last month called on businesses nationwide to order their workers to be vaccinated or lose their jobs.

The Public Service Department says disciplinary action can be taken against those who do not comply.

The inoculation push comes as President Joe Biden and other state and federal political leaders ratchet up pressure on unvaccinated Americans, some of whom object to mandates on religious or health grounds.