More than twenty Republican members of Congress have said that anti-free trade provisions within the Trans-Pacific Partnership (TPP) are holding them back from supporting it, and without their support the deal may not pass.

Several of those members have sent letters to President Obama’s lead adviser on trade, Michael Froman, regarding these concerns.

While TPP is intended to reduce tariffs, quotas, and trade barriers for thousands of products, some Republican members of Congress are concerned about a carve-out proposal for tobacco that they say will establish a dangerous new precedent.

Critics say that TPP currently allows American tobacco companies to be singled out to receive fewer protections and rights under the deal than those provided for other industries.

Senate Majority Leader Mitch McConnell (R., Ky.) has been outspoken about this concern, since tobacco plays a major role as the second highest agricultural export in Kentucky’s economy.

"As you work to complete Trans-Pacific Partnership (TPP) negotiations, I ask again that you not set a new precedent for future U.S. trade negotiations by negatively carving out a specific American agricultural commodity—in this case, tobacco," McConnell wrote to Ambassador Froman in July.

"It is essential as you work to finalize the TPP, you allow Kentucky tobacco to realize the same economic benefits and export potential other U.S. agricultural commodities will enjoy with a successful agreement," he said.

Other senators, including Sen. Thom Tillis (R., N.C.), Sen. Richard Burr (R., N.C.) and Sen. Orrin Hatch (R., Utah), have joined McConnell expressing their concern as well.

"In my conversations with other senators who would otherwise be inclined to support the TPP, I have emphasized the dangerous, precedent setting nature of a carve out and the fact that inclusion of such a term would run counter to the explicit instructions set forth in the TPA," said Tillis.

In addition to these senators, 17 members of the House Committee on Agriculture sent a letter to Ambassador Froman echoing these concerns. While citing opposition to the tobacco carve-out, members also wrote about market access to rice and dairy products. Lawmakers want greater access to Canadian markets for dairy producers in their states, as well as more access in Japanese markets for rice producers.

"We do, however, remain deeply concerned over the lack of meaningful market access in key markets for America’s rice farmers, and we are also deeply concerned by the lack of movement and transparency with respect to meaningful new, balanced market access for our nation’s dairy farmers," the members wrote. "In our estimation, more must be done in these regards."

Without support from these GOP members, the deal may not pass.

"If either the House or Senate rejects the TPP, however, the deal won’t go forward," according to an analysis from the Hill. "Just a handful of Republican votes against the TPP could keep it from winning a majority in the House, where most Democrats are expected to oppose it, with or without the tobacco provisions."

Proponents of the carve out for tobacco include anti-tobacco campaigners who want to regulate the commodity. "Unless nations take strong action, tobacco will kill one billion people worldwide in this century," said the Campaign for Tobacco-Free Kids. "This is a missed opportunity for the United States to lead the fight against this global epidemic."

But opponents of the carve-out say it will "undercut longstanding U.S. insistence that regulatory measures be based on evidence, including sound science, and encourage other countries to propose additional product-specific references."

"This is what happens when you make concessions to appease nanny-staters and liberals who have problems with the concept of free trade and free markets anyway," a Republican consultant who works on free trade issues told the Washington Free Beacon. "You end up with deals that are less free, and less politically tenable."