On Monday, Sen. Bernie Sanders (I-VT), the self-described socialist who is a potential 2016 presidential candidate, sent a scathing letter to U.S. Trade Representative Michael Forman regarding Trans-Pacific Partnership Free Trade Agreement (TPP).

Sanders’s letter signals that trade issues will again be a big issue among Democrats in the 2016 party, especially if Hillary Clinton enters the race.

In his letter, Sanders blasted the Trans-Pacific Partnership, which, as the Huffington Post notes, is “a major U.S. pact being negotiated with 11 Pacific nations” that “Sanders says will exacerbate income inequality and erode important regulations.” Sanders was most concerned about the secrecy surrounding the agreement and the access that special interest and corporations had to text even though some Members of Congress–like Sanders–did not.

“I have been very concerned that up to this date the text of this agreement has not been made public,” Sanders wrote. “The only text that I am aware of that has been made public so far has been through leaked documents, and I find what I read very troubling.”

As Sanders noted, “the TPP is poised to be the largest free trade agreement in history compassing 12 nations that account for nearly 40 percent of the global economy.” Sanders said the “TPP is not just another free trade agreement” because “it has broad economic and political implications for the entire economy, national sovereignty, healthcare, the environment, national security, and the Federal budget, among many other issues.”

Sanders also wanted answers about why Forman thinks 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” while “the people who will suffer the consequences of this treaty have been shut out of this process.”

“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 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 said.

Sanders demanded “a copy of the full composite bracketed text” so that staff and experts of his choosing could “analyze the relevant statutory and economic implications of this agreement.”

“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 context of any trade agreement being negotiated be made public at the request of any Member of Congress,” he added.

Left-wing Democrats who are urging those like like Sanders and Sen. Elizabeth Warren (D-MA) to run have blasted Hillary Clinton, “who was involved in TPP talks while secretary of state under Obama,” for her and her husband’s ties to Wall Street and crony capitalism.

As the Huffington Post notes, “the Clinton presidency signaled the Democratic Party’s full embrace of the financial elite, reversing the tough-on-banks platform implemented by Franklin D. Roosevelt under the New Deal.” The Clinton administration also ushered in the North American Free Trade Agreement (NAFTA) and the World Trade Agreement treaties, as the Huffington Post noted. Ross Perot described NAFTA as making “a giant sucking” sound that would send American jobs south of the border.

Activists on the left have been dissatisfied since Obama, who ran on a platform of “change” and promised to “turn the page” on the Bush and Clinton years, took office and immediately brought in top members of Clinton’s economic team.