DALLAS >> United Airlines says the number of employees facing termination for refusing to get vaccinated against COVID-19 has dropped nearly by half, to 320, after more of its 67,000 U.S. workers provided evidence of vaccination.

An airline spokeswoman said today that the declining number of potential firings shows that the company’s policy of requiring vaccinations is working.

United Airlines announced in August that it would require U.S. employees to get vaccinated, calling it an important safety measure. Employees faced a deadline this Monday to upload images of their vaccination cards showing that they had gotten at least one shot.

The airline said Tuesday that 593 employees faced termination. Today, United reduced that number and said that more than 99% of its workers have either become vaccinated or applied for a medical or religious exemption. People whose exemption requests are approved will be put on medical or other leave status and could lose their income.

“Our vaccine policy continues to prove requirements work,” spokeswoman Leslie Scott said in a statement. “In less than 48 hours, the number of unvaccinated employees who began the process of being separated from the company has been cut almost in half.”

Chicago-based United has the toughest vaccination policy among major U.S. airlines. Delta Air Lines is requiring vaccination or weekly testing, but will begin charging unvaccinated workers on the company health plan a $200 monthly surcharge starting in November.

American and Southwest have offered incentives for employees to get vaccinated, but have not indicated how they will comply with President Joe Biden’s order that employers with more than 100 workers require vaccination or weekly testing. Both airlines are based in Texas, where state officials are trying to limit mandates for vaccination and mask-wearing, and resistance to vaccination is stronger than in many other parts of the country.

Pilot unions at American and Southwest are resisting mandatory vaccination and are pushing instead for alternatives such as COVID-19 testing.

According to their union, 4,200 of American’s 14,000 pilots are not vaccinated.

United’s experience underscores that very few workers — usually fewer than 1% — are willing to quit or get fired because of vaccination mandates.

Novant Health, a North Carolina hospital system, said this week that about 175 of its 35,000 employees were fired for failing to get vaccinated. At Houston Methodist hospital system, about 150 of the 26,000 employees were fired in June.

Like mask-wearing, Biden’s order to require workers at large companies to get vaccinated or tested regularly has become a political issue. A poll released today by the Associated Press-NORC Center for Public Affairs Research found that Biden’s order is supported by three-fourths of Democrats but only one-fourth of Republicans.

Six United employees who got exemptions are suing the airline in federal district court in Texas, claiming they are being discriminated against because of medical conditions or religious beliefs. United has said the lawsuit has no merit.