WASHINGTON (MarketWatch) — Sen. Elizabeth Warren on Wednesday unleashed a fresh attack on a Pacific Rim trade deal being negotiated by the Obama administration, saying part of the proposed agreement raises “alarm bells” for everyone from conservatives to progressives.

In a call with reporters, the Massachusetts Democrat ripped the so-called investor-state dispute settlement process, a section of the proposed Trans-Pacific Partnership. President Barack Obama is pushing hard for the TPP, which is a proposed 12-nation deal Obama says will benefit American workers and businesses.

Warren, a member of the Senate Democratic leadership, disagrees, at least about the section she singled out in comments on Wednesday.

“ISDS allows foreign companies to challenge American laws and potentially to pick up huge payouts from taxpayers without ever stepping foot in an American court,” she said on a call organized by the group Alliance for Justice. Warren added companies that want to challenge U.S. laws could do so before an international tribunal.

Warren said that conservatives oppose the process for challenging U.S. sovereignty; libertarians dislike its effective subsidy to countries with weaker legal systems; and progressives oppose its allowing companies to weaken labor and environmental rules.

Obama and his advisers have said that TPP is an important counterweight to increasing competition from China, which isn’t part of the negotiations. The agreement would lower tariffs and set up new rules governing intellectual property, as well as procedures for resolving disputes between countries and multinational corporations.

Warren’s latest statement on the trade agreement comes as the White House is facing criticism about the proposed deal from a traditional ally. The Wall Street Journal reported Wednesday that dozens of major labor unions plan to freeze campaign donations to members of Congress to pressure them to oppose “fast-track” trade legislation sought by Obama. The move is part of the unions’ campaign against the TPP.

Obama and Republican leaders have identified trade as a major area of potential agreement. But some tea-party Republicans are skeptical of giving Obama expanded trade powers.