Senate Republicans are running into procedural problems as they try to advance their long-held goal to allow oil and gas drilling in the Arctic National Wildlife Refuge by attaching it to tax legislation.

Republicans, blocked by Democrats for years from permitting energy exploration in a portion of the Alaska refuge, are aiming to overcome those hurdles by considering the provision with the tax reform measure under budget reconciliation rules that allow it to avoid a filibuster and pass with a simple majority vote.

But the ANWR provision, as it was advanced by the Senate Environment and Natural Resources Committee, violates the Byrd Rule governing budget reconciliation, according to a Democratic source.

The source said the ANWR legislation directs the Interior Department to lease in a 1.5 million-acre section of the 19.5-million-acre refuge, known as the “1002 area,” using regulations and procedures the agency uses to lease in the National Petroleum Reserve in Alaska.

The National Petroleum Reserve is a separate 23.5-million acres of federal land in northwest Alaska already set aside for energy development.

Those rules must follow the National Environmental Policy Act, which is under the jurisdiction of the Environment and Public Works Committee, not the Energy and Natural Resources panel that considered the ANWR bill.

If that is true, the Democratic source said, the Interior Department must write its own rules for oil and gas leases in ANWR.

The Republican-controlled Congress in its budget resolution directed the Energy and Natural Resources Committee to create the ANWR legislation so that it raises $1 billion over a decade to help pay for tax reform.

The Byrd Rule requires that any bill approved by the Senate by a majority vote using the budget reconciliation process must not increase the deficit after 10 years. If the Interior Department has to write unique rules for ANWR, it could be time consuming and imperil the ability to raise $1 trillion in revenue within that 10-year budget window.

If the ANWR provision is removed from the tax reform bill, Republicans would need 60 votes for it to pass, a virtual impossibility.

The Senate voted Wednesday night to begin debate on the tax bill. Sen. Lisa Murkowski, R-Alaska, the chairwoman of the Environment and Natural Resources Committee, said earlier in the day she should would vote for the legislation. She told reporters she was not worried about fixing the ANWR provision so it could move forward with the tax bill.

“We will be able to resolve all this," Murkowski said. “I am not concerned.”