Democrats acknowledged Tuesday that their deadline for passing Wall Street reform was likely to slip past this week.

White House Press Secretary Robert Gibbs said at his daily press briefing that reform has become a matter of when not if, but he conceded "it will more likely get done the week they get back than this week."

That admission by the administration came as lawmakers prepared to re-open the conference committee later this afternoon to make final changes to the bill in order to ensure adequate Republican support to approve the changes to financial regulations in the Senate.

A spokesman for Senate Majority Leader Harry Reid (D-Nev.) also said Tuesday that it would be difficult to hold a vote on the Wall Street reform legislation this week.

With Sen. Robert Byrd (D-W.Va.) scheduled to lie in repose on the Senate floor almost all day Thursday and with work left to do on the legislation, spokesman Jim Manley told reporters that completing work would be "difficult but it's still possible."

President Barack Obama has said repeatedly he wanted to sign the reforms into law before the Fourth of July recess.

House and Senate conferees reopened their meetings Tuesday after Republicans expressed opposition to a $19 billion fee on financial institutions included in the conference report last week.

The meeting convened after Sen. Scott Brown (R-Mass.) released a letter outlining his objection to the bank fee, saying that he would oppose the bill as is.

Sen. Susan Collins (R-Maine), who like Brown voted for cloture on the original measure, echoed Brown's concerns with the fees but stopped short of saying it would prevent her from voting against the legislation.

Democrats are scrambling to find the votes to pass the measure. They lost one vote with the passing of Byrd. Democrats broke cloture in the Senate in May by a slim 60-40 margin.

Even though Brown withdrew his support, Manley said that Reid will still look to him for support.

"Sen. Brown is someone [Sen. Reid] can do business with and we look forward to getting his vote on these issues on the future," he said. 

Originally posted at 3:05 p.m. and updated at 3:34 p.m.