The Trump administration announced air traffic reductions of 10% will take effect next week at 40 major airports, and Frontier Airlines CEO Barry Biffle gave some unusual travel advice.In a now-deleted LinkedIn post, he urged passengers on Thursday to book additional tickets at a different airline, prompting backlash from consumers.“If you are flying Friday or in the next ten days and need to be there or don’t want to be stranded, I highly recommend booking a backup ticket on another carrier,” Biffle wrote. Frontier didn’t immediately respond to a request for comment.Meanwhile, the nation’s longest government shutdown threatens to wreck up to a fifth of fliers’ plans as the holiday travel season approaches.Thanksgiving, falling on Nov. 27 this year, is just three weeks away, and government officials are raising concerns about the potential for even deeper air traffic reductions.Transportation Secretary Sean Duffy said Friday that air traffic controllers will miss their second paycheck this coming Tuesday, if the government shutdown continues, which could cause cancellations to 15% or even 20% of flights. To make ends meet while not getting government paychecks, a growing number of federal workers in aviation are calling out sick to take on second jobs like waiting tables or becoming food delivery drivers for Uber, Duffy said.Most air traffic controllers can navigate missing one paycheck, but “virtually none” can handle missing two paychecks, he told Fox News. If more air traffic controllers come to work, then the Federal Aviation Administration (FAA) would be able to move the numbers “in the other direction,” Duffy said. But, as the shutdown continues, holiday plans are subject to the growing staff reductions.“Let’s end the shutdown, and let’s let the Congress debate their issues, but let’s not hold the American people hostage,” he said.The government shutdown started on Oct. 1 and is the longest in U.S. history, passing the prior record-long shutdown—during President Donald Trump’s first term between December 2018 and January 2019—on Wednesday. The shutdown entered its 38th day on Friday.An FAA order details that the agency will start with a 4% reduction in the flight operations at 40 major airports starting Friday, which will ramp up to 6% by Nov. 11, 8% by Nov. 13, and up to 10% by Nov. 14.By comparison, inclement weather cancels about 1%-2% of flights per day, according to The Weather Channel.After U.S. transportation officials ordered the commercial air traffic reduction, United Airlines, Delta Air Lines, and American Airlines canceled flights totaling between 3.5% and about 4% on Friday. Major carriers say they hope to notify passengers of cancellations anywhere from 24 to 72 hours in advance.But even when the government opens back up, Duffy said it will take some time for airlines to respond by putting flights back out for booking.“It can be days if not a week before we get back to full force flights when the shutdown ends,” he said.This story was originally featured on Fortune.com