Vaccines could soon be the ticket to traveling in the United States. Senator Dianne Feinstein has proposed legislation that would require all travelers taking domestic flights to present proof of vaccination or a negative COVID-19test. 

Under the U.S. Air Travel Public Safety Act, the secretary of Health and Human Services and the Federal Aviation Administration would be required to develop national vaccination standards and procedures for air travel.

It would also require the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices to make recommendations for COVID-19 vaccine use in health care settings and among health care personnel in other settings. 

"We know that air travel during the 2020 holiday season contributed to last winter's devastating COVID-19 surge. We simply cannot allow that to happen again," the California Democrat said.

"Ensuring that air travelers protect themselves and their destination communities from this disease is critical to prevent the next surge, particularly if we confront new, more virulent variants of COVID-19," she said, similar to requirements already in place for foreign travel. 

"It only makes sense that we also ensure the millions of airline passengers that crisscross our country aren't contributing to further transmission, especially as young children remain ineligible to be vaccinated."

University of California, Hasting Professor Dorit Reiss, who specializes in vaccine law, says the bill stands is constitutional and provides options for the unvaccinated.

"One of the challenges might be you need to include a religious exemption for those who oppose a COVID-19 vaccine. I don't think that will fly and here's why: it has a general exception," Reiss told CBS San Francisco. "People can provide a negative test instead. So people with religious objections to vaccination can instead go and get a negative PCR test. So there's already an exemption built in."

One traveler at San Francisco International Airport told the station the vaccine mandate would make her feel safer. "Now you're packed right next to someone. I don't want to drink on the plane, I don't want to eat on the plane. I'm not taking my mask off, I would feel much more comfortable knowing someone else is vaccinated," said Megan Barton, a nurse practitioner. 

"It's just science. Let's go with science people," traveler Kat Lake said. 

At least one state, Hawaii, requires vaccines or a negative COVID-19 test for domestic airline travelers. American Airlines has an app for people traveling to Hawaii or internationally to upload the necessary documents. 

The airline also said last month that it would not provide special leave to unvaccinated employees who have to quarantine due to COVID-19, Reuters reports.

JetBlue is highly encouraging crew members to get vaccinated for COVID-19, the airline says. The airline pays up to an additional 14 days sick time for any crew member diagnosed with COVID-19.

United Airlines was the first U.S. carrier to require vaccinations for all domestic employees, according to Reuters. This week, the company announced nearly 600 employeeswere being "separated from the company" for not complying.

Delta is also requiring employees to get vaccinated and last week said 82% had done so. Starting September 12, any employee who had not gotten vaccinated was required to take a COVID test each week.

However, pilot unions this week suggested vaccine mandates could cause shortages in the airline industry, CBS News transportation correspondent Errol Barnett reports. 

"If in fact pilots who are not vaccinated are put on unpaid leave or are terminated, that's more than 4,000 pilots in American Airlines that will not be able to fly," said Capt. Dennis Taje, spokesperson for Allied Pilots Association, which includes 15,000 American Airlines pilots. APA's vaccination rate is 70%, Barnett reports. 

APA and Southwest Airline's pilot association are both asking for exemptions before President Joe Biden's executive order mandating vaccines goes into effect.