WASHINGTON, May 19 (Reuters) - U.S. Senate Democratic

leader Chuck Schumer on Monday introduced a bill that would

prevent any foreign aircraft from being used as Air Force One,

the aircraft that transports the U.S. president.

Schumer introduced the "Presidential Airlift Security Act"

after news last week that President Donald Trump planned to

accept a $400 million airplane from Qatar, which legal experts

said raised a raft of questions about the scope of laws that

relate to gifts from foreign governments and are intended to

thwart corruption and improper influence.

Retrofitting the luxury plane offered by Qatar's royal

family would require security upgrades, communications

improvements to prevent spies from listening in and equipment to

fend off incoming missiles, experts said.

The costs were not known, but could be significant given

that Boeing Co's ( BA ) current effort to build two new Air Force

One planes exceeds $5 billion.

The bill introduced by the New York Democrat would prohibit

the Department of Defense from using any funds to procure or

modify foreign aircraft in order to serve as the president's air

transportation.

The measure is unlikely to become law, given that

Trump's Republicans hold majorities in the Senate and House of

Representatives, which would both have to approve it and

override a veto if Trump objected.

But it marked another effort by Democrats to oppose the

plan. Schumer last week vowed to block all of Trump's nominees

to the Justice Department until the agency reports what it knows

about Qatar's offer.

Multiple congressional Republicans

also raised concerns

about Qatar's offer.

Trump said it would be "stupid" for him to refuse the

offer.