US President-elect Donald Trump wants to cut government costs by cancelling the order for new planes to carry the American president.
Six weeks ahead of taking office, he tweeted: "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!"
The government has a contract with Boeing to build two or more new planes.
They would enter service around 2024.
Boeing shares fell more than 1 percent after the president-elect's tweet.
Mr Trump would not fly on the new planes unless he won a second term in the 2020 US election.
But the US Air Force has urged a faster schedule, saying the current jets are becoming too expensive to repair.
As president and commander-in-chief, Mr Trump will have the power to cancel the contract with Boeing for the new planes.
But if he does, it could cost the US taxpayer even more as the new president tries to save money. The US government has already signed a contract with Boeing for $US170m ($NZ239). Additional funding has also been earmarked for the two new planes.
The Government Accountability Office - an independent government auditor - estimates the final cost will be $US3.2bn. The planes are still in early design phases, though - much of the money has yet to be spent and has not had a chance to overrun the cost estimates.
Negotiation between Boeing and the US government could cut some of the costs, but if Mr Trump pulls out of the Boeing contract entirely the country may lose the money it is already contracted to pay.
Mr Trump now uses his own plane, but as president he would travel aboard Air Force One, which is equipped with special safety, defensive and communications equipment.
He later told reporters at Trump Tower in New York that Boeing was "doing a little bit of a number" and the cost was "ridiculous".
"We want Boeing to make a lot of money, but not that much money," he added.
The Government Accountability Office estimates that the project's overall cost will be $3.2bn, a figure that is expected to rise.
Boeing spokesman Todd Blecher, in a statement, said: "We are currently under contract for $170m to help determine the capabilities of these complex military aircraft that serve the unique requirements of the president of the United States.
"We look forward to working with the US Air Force on subsequent phases of the programme, allowing us to deliver the best planes for the president at the best value for the American taxpayer."