The Senate passed a bill by unanimous consent early Saturday morning that would bar U.S. airlines from participating in the European law to curb greenhouse gas emissions from the aviation sector.

The bill (S. 1956), sponsored by Sen. John Thune (R-S.D.), gives the secretary of the Transportation Department the authority to prohibit U.S. airlines from participating in the E.U. Emissions Trading System, or ETS.

The ETS's aviation directive, which applies to all flights into and out of Europe, took effect Jan. 1.

"Congress has sent a strong message to the E.U. that they cannot unilaterally impose an illegitimate tax on the United States," said Thune in a statement.

"The Senate's action today will help ensure that U.S. air carriers and passengers will not be paying down European debt through this illegal tax and can instead be investing in creating jobs and stimulating our own economy," he said.

The House, which passed similar legislation late last year, will now consider language approved by the Senate during the lame-duck session following the November presidential election.

Democratic co-sponsor Claire McCaskill (D-Mo.) praised the strong, bipartisan support for the "common-sense" bill.

Earlier this year, Transportation Secretary Ray LaHood and Secretary of State Hillary Rodham Clinton wrote letters to the European Union condemning the law, which requires all airlines to deposit allowances for the carbon emissions they produce starting in April of next year.

Indian and Chinese air carriers have also strongly opposed the aviation directive and refused to submit their 2011 emissions records to the European Union earlier this year in accordance with the law.

The White House has yet to take an official position on the U.S. legislation.

A European 'cash grab'?

U.S. airlines, pointing to their past and continued efforts to reduce carbon emissions independent of the E.U. law, have praised the Senate bill.

"Congress has spoken -- U.S. airlines should not be subjected to this illegal scheme that amounts to little more than a cash grab for the European Union as none of the funds collected are required to be used for environmental purposes," said Nicholas Calio, president and CEO of Airlines for America, the organization representing U.S. airlines.

Environmental groups, including the World Wildlife Fund and Environmental Defense Fund (EDF), countered that some airlines have made money on the scheme this year by raising their international fares in advance of the E.U. law taking full effect.

E.U. Parliament Environment Committee Chairman Matthias Groote called the U.S. effort to shirk the E.U. legislation "disrespectful and counterproductive" after the Thune bill passed through the Senate Commerce Committee in July.

An amendment included in the Senate legislation that passed this weekend requires the Transportation secretary to "reassess" the restriction on U.S. airlines if the E.U. law is amended, if the United States enacts a law to address aircraft emissions, or if an international agreement is reached.

U.S officials also urged for an international agreement, which is currently being negotiated in the International Civil Aviation Organization, or ICAO, a body of the United Nations.

Pressure for an international deal

Connie Hedegaard, the European climate commissioner, said, however, that the amendments provide no assurances the United States will actually work toward an international deal.

"It's not enough to say you want it, you have to work hard to get it done," she told Reuters. "That means that the U.S. needs to change its approach in ICAO and show willingness to actually seal a meaningful global deal that will facilitate action."

The E.U. directive was designed to reduce emissions from the aviation sector, which currently represent about 2 percent of global emissions but are on track to quadruple from 2005 levels by 2050 if left unregulated.

"The dispute has escalated with the Senate passage of this bill and the high likelihood that this bill become law," said Annie Petsonk, international counsel for climate and air with EDF. "So that puts more pressure on ICAO to come out with an international solution, which is what everyone says they want."

At the same time, since the secretary of Transportation only has to reconsider the law in the event that an international agreement is reached, it could create a counterincentive to reach an international deal, she said.

"If you're an airline and you do not want to limit your emissions, you do not want an E.U. law, and you do not want an international agreement," Petsonk said.