Republican leaders and the White House have both made it clear that they hope to pass trade agreements during the 114th Congress.

But Sen. Bernie Sanders (I-Vt.) on Monday vowed to throw cold water on those ambitions. He claimed that trade negotiations aren’t being conducted with proper oversight or transparency, and promised to introduce legislation that would compel the administration to be more forthcoming about deals it is hammering out.

In a letter dated Jan. 5, Sanders asked US Trade Representative Michael Froman for a “copy of the full composite bracketed text” of the Trans Pacific Partnership agreement. He wants the working agreement to be available to his aides and outside experts “so they can read the text, take notes, and analyze the relevant statutory and economic implications of this agreement.”

“Bracketed text” refers to a draft that includes proposals put forth by the US and other countries’ delegations. If Sanders does not see it, he said, he will try to force the USTR’s hand.

“If you choose not to release this information, I will be working with my colleagues in the Senate on legislation to require that the entire content of any trade agreement being negotiated be made public at the request of any Member of Congress,” he concluded. “And, I for one, will certainly make that request.”

Sanders said he has only seen the agreement’s language through leaked copies, and described what he read as “troubling.”

The Vermont senator, who is rumored to be gearing up for a 2016 Presidential campaign, argued that lawmakers “must have the opportunity to read what is in the TPP and closely analyze the impact” before renewing the President’s “fast-track” authority–a move that strips Congress of its right to amend trade deals.

Sanders also blasted the USTR, alleging that it has given corporate lobbyists an outsized role in crafting the TPP.

“It is incomprehensible to me that the leaders of major corporate interests who stand to gain enormous financial benefits from this agreement are actively involved in the writing of the TPP,” he wrote, “while, at the same time, the elected officials of this country, representing the American people, have little or no knowledge as to what is in it.”

Sanders requested that the USTR cite legal justifications for withholding the text of the agreement, if it declines to comply with his request. He also asked Froman to “explain why you think it is appropriate that the representatives of the largest financial institutions, pharmaceutical companies, oil companies, media conglomerates, and other major corporate interests not only have access to some of these documents, but are also playing a major role in developing many of the key provisions in it.”

Sanders asked the USTR to respond by Jan. 16.

The USTR did not respond to The Sentinel’s request for comment on Sanders’ letter or whether it intends to respond. In 2013, the USTR said that legislators are allowed to see US proposals, but did not mention that they are permitted to see the working agreement. Barbara Weisel, a USTR negotiator said, however, that she and her colleagues have spent “quite a bit of time” working with Congress.

She also said the USTR works with “stakeholders that represent lots of different interests” and denied that the business community is given special treatment. Rick Johnston, a Citigroup lobbyist speaking at a February 2013 panel with Weisel, however, said that the business community was “sort of part of a team” on negotiations, and that US trade officials have “been very, very forthcoming to the extent they can, in talking with us about this agreement, how this negotiation is going forward.” Another corporate lobbyist involved in the panel discussion–Steve Lamar, the executive vice president of the American Apparel and Footwear Association–also also praised the USTR for “experimentation” with stakeholders and “engagement and discussion going on at the rounds themselves”–events that many parties with an interest in the deal can’t afford to attend.

In December, President Obama expressed hope that the TPP would pass Congress, and said that “the odds of us being able to get a strong agreement are significantly higher than 50-50.” He added that the midterm election did not affect overall Congressional support for the deal “but we have to make the case and I think we can make a very strong case.”

If recent actions of Sanders and the Democrats he caucuses with are any indication, the President can expect the strongest resistance in Congress to come from the left. As The Sentinel reported, Sens. Tammy Baldwin (D-Wisc.), Ed Markey (D-Mass.) and Elizabeth Warren (D-Mass.) last month wrote Froman a letter, expressing concern that TPP compliance would undermine financial regulations. They also requested “all US proposals and bracketed negotiating texts relating to the three provisions discussed in this letter”–capital controls, market access, and investor state dispute settlements. The three Senators are expecting a response on Tuesday.

In December, Reuters reported that TPP negotiations would resume this month in the US or Australia. The other countries involved in the negotiations are Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, and Vietnam. Together, the twelve nations discussing the multilateral deal account for roughly forty percent of the global economy.