President Barack Obama's efforts to win final approval of a historic financial regulatory reform bill looked more complicated on Saturday after a Republican senator threatened to oppose it.

I was surprised and extremely disappointed to hear that $18 billion in new assessments and fees were added in the wee hours of the morning by the conference committee, Massachusetts Senator Scott Brown said.

He issued the statement after negotiators from the Senate and House of Representatives emerged from a marathon session early Friday morning with a final compromise on a bill that would bring about the most sweeping financial rules revamp since the 1930s.

The legislation would set up a new financial consumer watchdog, create a protocol for dismantling troubled financial firms and mandate higher bank capital standards -- all in an effort to avoid a repeat of the 2007-2009 credit crisis that hammered the economy and triggered taxpayer bailouts of floundering firms.

In May Brown was only one of four Republicans who voted for the Senate's financial regulatory reform package, which was approved, 59-39, with two members not voting.

Before that vote, Democrats had to overcome a Republican filibuster aimed at killing the bill and did that by the narrowest margin possible, 60-40.

Brown's possible defection from the bill increases the chance of a successful Republican filibuster this time unless Democratic leaders can find another vote.

Democrats control 57 seats in the Senate and Republicans 41. Two independents usually vote with the Democrats. It takes 60 votes to end a filibuster.

While I'm still reviewing the bill's details, these provisions were not in the Senate version of the bill which I previously supported ... I've said repeatedly that I cannot support any bill that raises tax, Brown said.

A spokesman for Senate Majority Leader Henry Reid had no comment on Saturday when asked if Brown's concerns posed a serious obstacle to final passage of the bill.

The three other Republicans that voted for the financial regulatory reform package in May were Senator Susan Collins and Senator Olympia Snowe, both of Maine, and Senator Charles Grassley of Iowa.

A spokeswoman for Grassley said he was still evaluating the conference report.

Two Democrats, Russ Feingold of Wisconsin and Maria Cantwell of Washington, voted against the Senate financial regulatory reform package in May.

Two other Democrats, Senator Robert Byrd of West Virginia and Senator Arlen Specter of Pennsylvania, did not cast a vote on the bill.

(Reporting by Doug Palmer; Editing by Bill Trott)

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