Leading House liberals will ask Speaker Nancy Pelosi (D-Calif.) on Thursday to help them block the pending Panama free-trade agreement in favor of a new U.S. trade model.

Populist Caucus Chairman Bruce Braley (D-Iowa), Trade Working Group Chairman Mike Michaud (D-Maine) and Congressional Progressive Caucus Co-Chairs Lynn Woolsey (D-Calif.) and Raúl Grijalva (D-Ariz.) are among those who penned a letter to Pelosi expressing concerns about the Panama deal. The group, along Rules Chairwoman Louise Slaughter (D-N.Y.), will unveil the letter to Pelosi at a press event Thursday afternoon.

The Bush-negotiated Panama agreement, which some senior Democratic aides have signaled could come up for an up-or-down vote in the next couple of months, “is not a new model on trade and does not represent the kind of change the American people are seeking,— the letter states.

High rates of unemployment coupled with concerns about Panama being a tax haven “will make any vote on this FTA difficult to justify,— the letter continues. “We believe this is a historic opportunity to push forward a new trade model that will benefit workers and businesses.—

The group says Pelosi “can be an effective advocate for our cause— and asks for “an open, honest dialogue— with her on the issue.