A vote could come as early as Wednesday night.
Even after months of intense lobbying by the president and administration trade officials, it was not clear if supporters had the needed votes.
Rep. Gil Gutknecht (R-Minn.) said Wednesday evening that he will vote against the proposed Central American Free Trade Agreement, making him the only Republican from Minnesota to oppose the deal.
"Unfortunately, when you compare the upside and potential downside, I believe the agreement has three potential fatal flaws," Gutknecht said in a statement. "They are fixable, but they couldn't be fixed before this vote."
Rep. Jerry Moran (R-Kan.) has questions about CAFTA and whether Central American trading partners may continue to erect barriers against U.S. products despite the agreement.
Moran also is using his vote as leverage to discuss other trade issues with the White House. When President Bush called Moran to the White House last week to talk about his vote, Moran urged the administration to ease restrictions on trade with Cuba and put more pressure on Japan to lift its sanctions on imports of U.S. beef.
Moran's Kansas colleague, Democratic Rep. Dennis Moore, traditionally a free trade advocate, remains concerned about the effect on U.S. jobs and whether labor standards would be enforced oversees, said spokeswoman Christie Appelhanz.
The agreement eventually would eliminate tariffs and other trade barriers between the U.S. and Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and the Dominican Republic. The trade deal was signed a year ago and approved by the Senate last month.
Kansas Republican Reps. Jim Ryun and Todd Tiahrt both plan to cast votes for CAFTA.