This vote was on a motion to table (kill) an amendment delaying construction of the controversial Keystone XL pipeline until federal law had been changed to ensure the oil it carries is taxed like other petroleum products.

Sen. Ed Markey (D-MA) offered the amendment during consideration of a bill authorizing construction of the pipeline. Most oil is subject to an 8-cent-per-barrel federal excise tax that funds clean-up efforts in the case of a spill. However, because oil from Canada’s “tar sands” is actually a mixture of soil and bitumen – it is extracted through strip mining rather than drilling – it was exempt from this tax under existing federal law. Sen. Markey’s amendment would have made approval of the pipeline contingent on a change in that policy – ensuring the oil carried through the Keystone XL was subject to the tax.

However, before the amendment came to a vote, Sen. Mitch McConnell (R-KY) offered a “motion to table” it. If successful, this motion would prevent Sen. Markey’s amendment from getting an up-or-down vote, effectively killing it.

Supporters of Sen. Markey’s amendment argued that the existing “loophole” in federal tax law would put American oil producers at a disadvantage. It would also leave taxpayers on the hook for any spills on the Keystone XL pipeline, they said, since the company would not have to contribute to the clean-up fund.

“If spilled into the environment, oil produced from tar sands is just as damaging as oil produced by other means, if not more so,” Sen. Carl Levin (D-MI) said in 2014. “Surely producers of oil from tar sands should help contribute to the costs of cleaning up these spills – just like producers of other oil must do.”

Supporters of the motion to table did not explain their opposition to Sen. Markey’s amendment; in fact, earlier in the debate, Sen. Lisa Murkowski (R-AK) expressed support for a policy that would subject the Keystone XL’s oil to the tax. However, she argued, rather than adding the policy to the underlying bill, the Senate should give the House of Representatives a chance to add it, since the Constitution requires revenue-raising legislation to originate in the lower chamber.

“This is important because right now we have a legitimate but unintended loophole on the books, and it is also a matter of fairness because conventional oil pays into the trust fund,” Sen. Murkowski said, adding that lawmakers should correct the issue “legitimately through the Constitution.”

The Senate agreed to the motion to table by a vote of 53-42. Voting “yea” were 51 Republicans and 2 Democrats. Voting “nay” were 42 Democrats. As a result, the Senate defeated the effort to allow an up-or-down vote on an amendment delaying construction of the controversial Keystone XL pipeline until federal law had been changed to ensure the oil it carries is taxed like other petroleum products.