Republicans in the Wisconsin state Senate have introduced a bill that would require employers in the state to allow proof of a previous COVID-19 infection as an alternative to vaccination and testing.

The bill is likely to be vetoed by Democratic Gov. Tony Evers, according to a report in the the Wisconsin State Journal, but it highlights a new front in the battle over vaccine mandates at the heart of the nation's COVID-19 politics. 

Republicans have challenged Biden administration vaccine rules for businesses and health care workers in court, threatening their long-term validity. 

As court fights move forward, Biden's initial vaccination or testing mandate went into effect on Monday. 

A public hearing on the Wisconsin bill took place on Tuesday, the State Journal reported. Similar bills have been offered in other states by proponents who argue a previous COVID-19 infection should count toward immunity.

The National Vaccine Information Center, an organization that advocates against vaccine mandates, testified at Tuesday's hearing in the Wisconsin Senate, where two witnesses from the group said natural immunity was at least as effective as vaccination.

Public health experts have pressed for more Americans to get vaccinated, arguing vaccinations are the best way out of the pandemic. The Biden administration has also called for booster shots for most of the public as the highly contagious omicron variant sweeps through the nation. 

Omicron has affected people who have been vaccinated and who have previously had COVID-19.

Data does suggest that omicron is not leading to severe cases of COVID-19 or hospitalizations and death for vaccinated people.

Ajay Sethi, director of the Public Health master's program at UW-Madison, told the Wisconsin State Journal that if the Wisconsin Senate bill becomes law, “you would have people who falsely believe that they are protected against reinfection. And the science continually shows that people who are unvaccinated, even if they've had COVID before, are more likely to be hospitalized compared to people who are vaccinated and haven't had COVID before.”