House Republican leaders continued aggressively lobbying colleagues wavering on whether to support Speaker John Boehner's plan to raise taxes on people making more than $1 million annually.

With just about an hour to go before the scheduled vote, some news reports suggest at least 25 House Republicans are leaning towards voting against the plan, which would present a major political blow to Boehner's efforts to provide an alternative to proposals put forth by President Obama.

During earlier votes, House Majority Whip Kevin McCarthy (R-Calif.) and House Majority Leader Eric Cantor (R-Va.) were seen speaking with several potential "no" votes, including Reps. Trey Gowdy (R-S.C.) and Vern Buchanan (R-Fla.).

Conservative Republicans have expressed concerns about voting for a bill that would raise taxes, even if only .18 percent of taxpayers are likely to be affected.

A clutch of more conservative members, including Reps. Ron Paul (R-Texas), Walter Jones (R-N.C.), Jason Chaffetz (R-Utah), Justin Amash (R-Mich.) and Joe Walsh (R-Ill.) have clustered in seats along the center aisle. Rep. Cathy McMorris Rodgers (R-Wash.), soon to be the fourth-ranking House Republican, was seen speaking with several of these conservatives, including Rep. Raul Labrador (R-Idaho), who said earlier Thursday that he is strongly opposed to Boehner's "Plan B."