Centers for Disease Control and Prevention (CDC) director Dr. Rochelle P. Walensky said at a White House news conference on Tuesday that the government was considering a range of measures to make international travel as safe as possible, including “pre-departure testing closer to the time of flight, and considerations around additional post-arrival testing and self-quarantines.” There are further reports today that the White House and the Department of Health and Human Services are reviewing a draft letter from the CDC on the new restrictions.

Since the U.S. first reopened its borders on Nov. 8, the government has had quite relaxed rules on those allowed to enter the country, requiring only a negative COVID-19 test for vaccinated travelers taken up to three days before their flight—a stark difference from countries like Australia or China, which have completely barred entry or require 14 to 28 days of quarantine in a hotel after arrival.

The U.S. markets didn’t seem to mind the idea of tougher restrictions, with S&P 500 and Nasdaq 100 futures up 1% and 0.7% respectively in premarket trading Wednesday. But the rules will affect those flying in for the holiday season. Here are four ways that travel could change your holiday plans:

Shorter testing windows

Before you touch down in the U.S., the Biden administration is likely to require a negative COVID-19 test taken just one day before boarding flights—regardless of vaccination status. First reported by the Washington Post, there is no clearer news on what kind of test will be necessary, but travelers coming to the U.S. will have to time tests more carefully to ensure they are let onto flights.

Under current restrictions, the U.S. requires incoming travelers to get a test up to three days before departure for vaccinated travelers, and one day for unvaccinated ones.

Post-arrival testing

Another restriction under consideration would require travelers to take a second or even third COVID-19 test within three to five days of arrival. This measure has been widely used across Europe and in other countries with tougher entry requirements, where travelers must take more COVID-19 tests after they land in order to ensure any delayed onset of COVID-19 is caught before cases spread on domestic soil.

This could increase the price of holiday travel.

Quarantining upon arrival

Alongside a retesting program, the U.S. government is also reportedly considering requiring travelers, including U.S. citizens, to quarantine for at least seven days after landing—regardless of the outcome of the COVID-19 tests they have taken. Those who flouted the rules could face fines, a significant escalation in U.S. COVID rule enforcement.

This would mean all family members flying in for the holiday would have to self-isolate as soon as they arrive. In order to attend a Christmas family gathering, arriving travelers might need to touch down by Dec. 17 at the latest to be able to legally participate in the holiday fun.

Banning entry

The U.S. could close its borders to more countries with a high Omicron threat. Since Monday, the door has already closed on Botswana, Eswatini, Lesotho, Malawi, Mozambique, Namibia, South Africa, and Zimbabwe. This is seen as unlikely, however, as President Biden noted he does not expect the U.S. to impose such travel restrictions on new countries soon.