Senate Democrats threatened to block Majority Leader Mitch McConnell’s efforts to start debate on a contentious Trade Promotion Authority bill unless the Kentucky Republican guarantees that a customs bill with currency manipulation provisions gets a vote.

Democratic Whip Richard J. Durbin said some in his caucus want the customs bill included in a substitute McConnell would offer after a cloture vote on a bill serving as a vehicle to send the trade promotion bill, also known as fast-track, to the House. Durbin said other Democrats would be satisfied if McConnell agrees to put the customs bill on the Senate floor in the near future.

The maneuvering reveals the difficulty the Senate may have in passing the trade-promotion bill. 

“I’d rather have it all in one bill but that’s unlikely. We want to see what the alternative is,” Durbin told reporters Monday evening. “People want to know what they are voting for and so far Sen. McConnell has been very furtive.”

 Sen. Orrin G. Hatch, R-Utah, the chairman of the Senate Finance Committee, who shepherded the bill through committee, said he was unsure if cloture will be invoked Tuesday.

“We’ll have to see what happens. They (Democrats) are playing a very dangerous game,” Hatch said.  

Durbin said McConnell has to ask himself if he has the 60 votes to invoke cloture. McConnell would need to hold all 54 Republicans and pick up six votes from Democrats and the chamber’s two independents.

“That’s questionable,” said Durbin, from Illinois.

Democrats in particular want the customs bill made law because it includes a currency manipulation provision with enforcement requirements by Sen. Charles E. Schumer, D-N.Y. The language would expand the definition of export subsidies to include currency undervaluation by trading partners that causes harm to U.S. companies. The United States would have to impose import duties on goods the Commerce Department identifies as benefiting from the undervaluation. Some lawmakers accuse countries such as China of keeping its currency artificially low to encourage exports.

White House spokesman Josh Earnest said Monday that some Democratic-backed currency proposals could undermine the Federal Reserve’s independence.

The Senate Finance Committee approved the trade promotion legislation after Chairman Orrin G. Hatch, R-Utah, and ranking member Ron Wyden, D-Ore., along with House Ways and Means Chairman Paul D. Ryan, R-Wis., agreed on a draft text.

But Wyden also wants a guarantee or an agreement that the customs bill, the Trade Promotion Authority bill (S 995), the Trade Adjustment Assistance and a three-bill package that includes the African Growth and Opportunity Act, Generalized System of Preferences and reauthorization of a trade program for Haiti move through Congress and become law, his spokesman Keith Chu said, adding that the bills don’t have to be part of one package.

Hatch let his irritation show Monday, when he complained that Democrats’ conditions violated his agreement with Wyden. But Hatch later said he felt better about Wyden’s terms.

Sen. Bill Nelson, D-Fla., voted for the trade promotion bill in the Finance Committee but said Monday he would not vote for cloture if the four bills aren’t part of a package. “If he decides to leave out some of the reforms we put in the customs bill, then I will not vote to advance the bill,” Nelson said.

Steve Dennis contributed to this story.