Democratic former Sen. Russ Feingold railed against trade deals like NAFTA and the Trans-Pacific Partnership to labor union members on Monday, pledging to oppose "lousy, unfair" deals if re-elected.

Feingold's speech at the Wisconsin AFL-CIO's biennial convention in downtown Madison centered on trade as he drew a contrast between himself and Republican Sen. Ron Johnson, who has not said whether he supports or opposes the TPP.

Johnson, who voted to give the president fast-track authority on trade deal negotiations, has supported such deals in the past. His campaign accused Feingold of making a snap decision, arguing Johnson is taking time to consider the text of the deal and opinions of his constituents.

Johnson confirmed in July he doesn't plan to share his stance until he takes a vote on the deal. Feingold came out against it in May 2015.

Johnson's campaign argued there are major differences between the draft that was available when Feingold came out against the TPP and the final version made public in November.