It is one of the largest the US defence department has issued in recent years.
Several senators said the contract would take jobs from US citizens at a time when the nation's economy is widely perceived to be in crisis.
"The Airbus contract is a European stimulus plan subsidised by the American taxpayer"
"The Airbus contract is a European stimulus plan subsidised by the American taxpayer," Patty Murray, senator for Washington state, was quoted by AFP as saying.
"We need to be investing in the American aerospace industry and the high-wage, high-skill jobs it supports."
Hillary Clinton, the Democratic presidential candidate, also said she was "deeply concerned" by the decision, while Democratic rival Barack Obama also expressed disappointment about the move, the Wall Street Journal newspaper reported.
However, legislators from the US state of Alabama, where EADS is to assemble the tankers, denied that American jobs would be lost.
"In reality, what we're talking about is the insourcing, into America, of an aircraft production centre that would bring 2,500 jobs to our area and 5,000 to the state," Jeff Sessions, a Republican senator, said on Monday.
"A vigorous competition reduced the [price of the] bids substantially."
EADS joined up with US aerospace group Northrop Grumman to outbid US defence manufacturing giant Boeing for the contract, which would replace aging KC-135 tankers built by Boeing.
Congress had scrapped a previous air force plan to lease 100 Boeing 767 tankers after a former senior air force official was imprisoned for negotiating a job with Boeing while working on the deal.
The scandal emerged during an investigation by John McCain, the Arizona senator and Republican presidential frontrunner.
The air force's handling of the deal was monitored by an independent team of military and civilian analysts.