NEW YORK (Reuters) – U.S. President-elect Donald Trump on Tuesday urged the government to cancel an order with Boeing Co to develop a revamped Air Force One – one of the most prominent symbols of the U.S. presidency – saying costs were out of control.

Trump, who takes office on Jan. 20, pledged during his unconventional campaign for the White House that he would put his skills as a businessman to work for taxpayers, and had griped about the cost of President Barack Obama’s use of the presidential aircraft.

It was not immediately clear what prompted his complaint about Boeing on Tuesday, but a spokesman said that Trump was sending a message that he intends to save taxpayers’ money.

“Boeing is building a brand new 747 Air Force One for future presidents, but costs are out of control, more than $4 billion. Cancel order!” Trump said on Twitter before making a surprise appearance in the lobby of Trump Tower in New York, where he amplified his comments.

“The plane is totally out of control. I think it’s ridiculous. I think Boeing is doing a little bit of a number. We want Boeing to make a lot of money but not that much money,” he told reporters.

It was not clear what Trump’s source of information was for the cost. The budgeted costs for the Air Force One replacement program are $2.87 billion for the fiscal years 2015 through 2021, according to budget documents.

A March 2016 report from the Government Accountability Office, a watchdog agency, estimated the total cost of the two 747’s, which have to be extensively modified so they can function as an airborne White House, was estimated at $3.2 billion.

Boeing has not yet been awarded the money to build the two proposed Air Force One replacements. It is currently working on engineering and designing the aircraft.

“We are currently under contract for $170 million to help determine the capabilities of these complex military aircraft that serve the unique requirements of the President of the United States,” the company said in a statement.

“We look forward to working with the U.S. Air Force on subsequent phases of the program allowing us to deliver the best planes for the president at the best value for the American taxpayer.”

Boeing shares dipped after Trump’s tweet and were down around 0.5 percent at midday. Shares of several other major defense contractors were also lower.

NOT A ‘VANILLA’ JUMBO JET

A wealthy real estate developer, Trump used his own Boeing 757 to campaign around the country, pledging to shake up Washington.

A Trump spokesman said that his comments about the plane reflected the president-elect’s desire to keep down costs across the board, and so save taxpayers’ money.

The U.S. Air Force, which operates the presidential planes, first announced in January 2015 that Boeing’s 747-8 would be used to replace the two current planes that transport the U.S. president.

The Air Force has two planes in case one breaks down or needs to be taken out of service for maintenance. The two replacements for the current Air Force One planes are scheduled to be in service by the 2024 fiscal year.

Boeing officials were caught off guard by Trump’s comments since the company is simply meeting requirements mapped out by the Air Force in consultation with the White House, said defense consultant Loren Thompson, who has close ties to Boeing and other companies.

The cost of the planes is high because of the unique security requirements and communications equipment, Thompson said.

“Air Force One has unique mission requirements, including possibly having to operate in a nuclear war,” Thompson said. “Of course it’s not like buying a vanilla Boeing jumbo jet.”

U.S. presidents have used Boeing planes since 1943, according to the company’s website.

The 747-8 planes, 240 feet long (73 meters) long with a wing span of 224 feet (68 meters), can fly direct from Washington to Hong Kong, 1,000 miles (1,600 km) farther than the current Air Force One.

In a September 2015 Rolling Stone profile of Trump, early on in his presidential campaign, he was quoted as gushing about the capabilities of his own Boeing plane.

“I bought this from Paul Allen and gutted it top to bottom. It’s bigger than Air Force One, which is a step down from this in every way. Rolls-Royce engines; seats 43. Did you know it was featured on the Discovery Channel as the world’s most luxurious jetliner?” he said.

(Additional reporting by Emily Stephenson, Mike Stone, Susan Heavey, Andrea Shalal and Doina Chiacu in Washington and Steve Holland, Alana Wise, Jeffrey Dastin, and Lewis Krauskopf in New York, and Alexander Cornwell in Dubai; Writing by Roberta Rampton; Editing by Frances Kerry)

IMAGE: Air Force One with U.S President Barack Obama aboard lands at the Eleftherios Venizelos International airport in Athens, Greece, November 15, 2016. REUTERS/Michalis Karagiannis