Sen. Scott Brown, a key vote considered necessary to pass regulatory reform, said Tuesday he would not support the final bill unless a provision to tax banks is removed from the legislation.

"I am writing you to express my strong opposition to the $19 billion bank tax that was included in the financial reform bill during the conference committee," Brown wrote in a letter to House Financial Services Committee Chairman Barney Frank and Senate Banking Committee Chairman Chris Dodd. "This tax was not in the Senate version of the bill, which I supported. If the final version of this bill contains these higher taxes, I will not support it."

The Massachusetts Republican had warned Friday that he was considering dropping his support for the bill, but had not yet been definitive on the issue.

Democrats had been counting on Brown's support to ensure the 60 votes necessary for a procedural vote in the Senate to move to final passage. Without him, they will need to convince at least one of two Democratic defectors - Sens. Russ Feingold and Maria Cantwell - to switch sides. Feingold said Monday he would not vote to move the bill forward.

The other three Republicans who voted for the bill in the Senate - Sens. Chuck Grassley of Iowa and Olympia Snowe and Susan Collins of Maine - must also maintain their support.

For his part, Brown said the bank tax would be passed "onto the millions of American consumers and small businesses who rely on major U.S. financial institutions for their checking, ATM, loans or other services."

"Imposing this new tax is the wrong option," Brown wrote. "Our economy is still struggling. It is wrong to impose higher taxes and ignore the impact it will have on our economy without considering other ways we might offset the costs of the measure."

The conference committee added the tax provision to comply with House rules that say a final bill must not incur new costs to the government. The tax, which would collect $19 billion from large banks over five years, was imposed to pay for the estimated cost of the reform legislation.

Brown suggested that the bill impose spending cuts instead.

"There are hundreds of billions in unspent federal funds sitting around, some authorized years ago for long-dead initiatives," he wrote. "Congress needs to start to looking there first, and I stand ready to help."

It was unclear when the House would take up the bill with the situation in the Senate up in the air.

The Senate's schedule is further compounded by memorial plans for Sen. Robert Byrd, who died on Monday. The Senate had been expected to vote on regulatory reform on Thursday, but that no longer appears possible.

Byrd is expected to lie in state in the chamber on Thursday and his funeral, which will be attended by much of the Senate, is expected to be held Friday in West Virginia.

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