US lawmakers will examine the decision to award a huge US Air Force contract to European firm EADS and its partner, Northrop Grumman.
The move was seen as a blow to Boeing, which missed out on a deal to supply air tankers potentially worth up to $40bn (£20bn).
US House Speaker Nancy Pelosi said she wanted the Air Force to explain how the deal met long-term military needs.
The Pentagon contract for 179 new aircraft was announced on Friday.
It is one of the largest deals of recent years.
Best value
"The Air Force's decision to award the contract for a much-needed modernisation of the nation's aerial tanker fleet to Northrop Grumman and Airbus raises serious questions that Congress must examine thoroughly," Ms Pelosi said in a statement.
EADS and Northrop Grumman are planning to assemble the aircraft in Alabama. Parts including the wings will be built in the UK by Airbus.
The Pentagon has said that the EADS bid offers the best value.
Home-grown
Boeing emphasised its home-grown credentials while lobbying for the contract.
"The best for America's war fighters and America's workers," Boeing claimed in advertising running in the days leading up to the announcement.
But EADS and Northrop Grumman emphasised that the assembly work would be carried out in the United States, where the project would create or support 25,000 jobs.
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