United Airlines will reduce flights, freeze hiring and ask employees to volunteer for unpaid leave as the airline struggles with weak demand for travel because of the new virus outbreak.

United said Wednesday that starting in April it will reduce passenger-carrying capacity 20 percent on international routes and 10 percent in the U.S. — the first airline to cut domestic flying. United officials said they will temporarily ground an unspecified number of planes.

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The moves by United are the clearest sign yet of the financial harm to U.S. airlines from the virus, which has already led them to suspend flights to China and reduce service to other countries.

United announced the cuts shortly after several airline CEOs met at the White House with President Donald Trump and Vice President Mike Pence. The administration is seeking the airlines' help in tracing travelers who might have come in contact with people ill with COVID-19.

The virus “is affecting the airline business, as it would,” Trump said after the meeting. "A lot of people are staying in our country, and they’re shopping and using our hotels in this country. So from that standpoint, I think probably there is a positive impact, but there is also an impact on overseas travel, which will be fairly substantial.”

Acting Homeland Security Secretary Chad Wolf, who was also in the meeting, said his agency has screened more than 53,000 people “and prevented a number of folks from coming into the country” largely because of cooperation from the airlines. He did not elaborate.

Wolf said the administration wants additional information about travelers so that public-health agencies can “get in touch with them, looking for a few more pieces of information and data from them.”

The airline CEOs said their companies have stepped up cleaning procedures to help protect passengers and employees from the virus.

United's decision to reduce flying came shortly after Germany's Lufthansa announced it would park 150 planes because of falling demand.

Airline bookings have slumped as the outbreak has spread beyond China to the U.S. and dozens of other countries. Some large corporations have banned or limited employee travel, and a few large business conferences have been canceled.

At Chicago-based United, the deepest reductions in flying will be between the U.S. and Asia — a cut of 50 percent. United, like Delta and American, suspended service to mainland China and Hong Kong last month. United will also chop 10 percent from its schedule between the U.S. and Europe, 5 percent to Latin America.

United officials said they don't plan to abandon service to any U.S. cities, but they will eliminate some routes as part of the 10 percent cut in the April schedule for domestic service. For example, the airline will stop flying from Chicago to Eugene, Oregon, but it will continue to serve Eugene from San Francisco and Denver. It will also reduce the number of daily flights on some routes.

United's top executives said they expect those reductions to extend into May, but they have not determined what to do after that — it will depend on bookings over the next few weeks.

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CEO Oscar Munoz and President Scott Kirby said hiring has been frozen at least through June 30 except for critical positions. And they said in a letter to employees that beginning immediately, U.S.-based workers could apply for a voluntary, unpaid leave of absence or a reduced schedule. Officials said the company does not plan layoffs.

“We sincerely hope that these latest measures are enough, but the dynamic nature of this outbreak requires us to be nimble and flexible moving forward in how we respond,” Munoz and Kirby said in their letter.

Southwest Airlines has not reduced flying and doesn’t have immediate plans to do so, said spokesman Brad Hawkins. American Airlines declined to comment on its plans. Delta Air Lines did not immediately respond for comment.