Both business groups and organized labor groups put senators on alert Monday that they're closely watching a procedural vote today on Wall Street reform.

The U.S. Chamber of Commerce, as well as the AFL-CIO and a number of labor organizations, sent letters to senators urging them to either vote against or for, respectively, a motion to begin debate on the financial reform bill.

"The Chamber believes that, in its current form, S. 3217 does not achieve the financial regulatory reform that is needed for the economic growth and job creation for a prosperous 21st century economy," Chamber President R. Bruce Josten wrote in a letter on Monday. "The Chamber may consider votes on, or related to, S. 3217 in our annual How They Voted Scorecard, including the vote on the motion to proceed."

AFL-CIO government affairs director Bill Samuel, conversely, warned senators to vote to advance the bill, arguing that failing to do so would be a slap to working class Americans.

"There is no justifiable reason to further delay consideration of comprehensive financial reform legislation that is critical to the economic survival of our country," Samuel wrote to lawmakers.

The flurry of letters represent the high-stakes in this evening's vote, as well as the closely-watched debate that's unfolded in the Senate in recent weeks on Wall Street reform legislation.

Senators will vote just after 5 p.m. to formally take up the financial reform bill. If all 41 Republicans oppose it, as some leading Republicans have suggested they would, it would leave Democrats a vote short from beginning debate on the legislation.

Leaders of both parties have said a deal is unlikely before then, though negotiations continue toward a bipartisan solution on the legislation.

In the meanwhile, Democrats and Republicans have continued to keep the pressure on each other before the vote.

To that end, Senate Majority Leader Harry Reid's (D-Nev.) office released a letter Monday signed by 30 left-leaning groups urging senators to support the motion to proceed.

"If policy differences still exist, now is the time to work them out in the public arena, and then vote," the groups said. "A filibuster would rob the taxpayers of their right to know what their elected representatives truly believe and support when the proverbial chips are down."