The number of Republicans who say they will vote down a three-week extension of government funding swelled Tuesday, as conservatives railed against the measure for not doing enough to cut spending.

Over a dozen House Republicans have said they will oppose a continuing resolution (CR) set for a House vote Tuesday afternoon, nearly half the number it would take to bring down the measure if no Democrats were to support it. Several others have indicated they could vote against it.

Five Senate Republicans also said they would also oppose the continuing resolution, which would prevent a shutdown after Friday by extending funding for another three weeks. The measure cuts $6 billion from existing spending.  

Even though GOP leaders have predicted the measure will pass — Speaker John Boehner (R-Ohio) said Tuesday he is "confident" — opposition is expected to be significantly higher than it was to the first stopgap measure passed at the beginning of the month. 

The growing number of defectors demonstrates that conservative back-benchers are putting increased pressure on GOP leaders to make significant spending reductions through a long-term government funding measure.

House Republican leaders have suggested this will be the last short-term funding measure they put forth, setting up a final showdown with Democrats on spending in the coming weeks.

Here are the House members who have said they will vote against the short-term CR: 

Rep. Jason Chaffetz (Utah)
Rep. Michele Bachmann (Minn.)
Rep. Mike Pence (Ind.)
Rep. Steve King (Iowa)
Rep. Jim Jordan (Ohio)
Rep. Jeff Flake (Ariz.)
Rep. Jeff Duncan (S.C.)   
Rep. John Fleming (La.)
Rep. Allen West (Fla.)
Rep. Louie Gohmert (Texas)
Rep. Tim Huelskamp (Kan.)
Rep. Justin Amash (Mich.)
Rep. Tom Graves (Ga.)
Rep. Dennis Ross (Fla.)

Reps. Walter Jones (N.C.) and Ron Paul (Texas) also voted against the first short-term CR, but have not  announced if they will oppose the latest one. They were joined by only four other House Republicans. The meaure passed 335-91 with over 100 Democrats voting for it.

Here are the five senators who are no votes:

Sen. Marco Rubio (Fla.)
Sen. Jim DeMint (S.C.)
Sen. Rand Paul (Ky.)
Sen. Mike Lee (Utah)
Sen. Orrin Hatch (Utah)

Five voted against it last time; the latter three plus Sens. Mike Crapo (Idaho) and Jim Risch (Idaho). The measure passed 91-9.

-- This post was updated at 12:23 p.m.