South Carolina Republican Rep. Jeff Duncan is dropping his co-sponsorship of an immigration bill House Republicans have been quietly working to include in the upcoming Department of Defense authorization bill, saying the language should never have been considered to be added to the unrelated measure.

Late Wednesday, Duncan said he hadn’t been aware of efforts by the bill’s author, California Rep. Jeff Denham (R-CA), to add the language to the National Defense Authorization Act (NDAA) – and that if it were added, “NDAA would lose my vote as well.”

At issue is a proposal to allow so-called DREAMers to obtain permanent legal residency by joining the military.

Sophomore Republican Rep. Jeff Denham of California, a close ally of GOP Whip Kevin McCarthy, is leading the push to add the text of his “ENLIST Act” to the NDAA, which could come to the House floor as early as next month.

Duncan is the first of 42 co-sponsors to rescind his support since Breitbart News reported of the effort to add the proposal to the NDAA bill. The secretive effort has set off a panic among top immigration hawks that inclusion of the language could open an immigration Pandora’s box, paving the way for a broader immigration bill.

The South Carolinian’s support for the Denham bill was particularly important because Duncan is a high-profile conservative.

Reps. Mick Mulvaney and Trey Gowdy – the latter of whom is the chairman of the immigration subcommittee on the House Judiciary Committee – are two other South Carolina Republican cosponsors who could provide conservative heft to the Denham effort.

In addition to House leadership, two key GOP chairmen are key to whether Denham succeeds. California Rep. Buck McKeon, chairman of the House Armed Services Committee, is helming the effort to draft the NDAA bill. Rep. Bob Goodlatte, chairman of the House Judiciary Committee which has jurisdiction over the immigration issue, could pull rank and topple the effort as well.

Goodlatte said Wednesday “we’re working on it.” A House Armed Services committee aide said McKeon hadn’t committed to including the language in the NDAA bill.

Key proponents of a comprehensive immigration bill said they support Denham’s effort but that it’s not part of a broader push for amnesty.

But top immigration hawks ripped the proposal as ill-conceived and a clear effort to build momentum for a comprehensive immigration bill.

“Everything by the illegal alien allies is part of a bigger play,” Rep. Mo Brooks said Wednesday, adding, “There is always the risk that those in Washington that wish to betray the American people on behalf of illegal aliens will slip some language into some place that opens the floodgates to the detriment of American workers.”

Update: Duncan wrote a Facebook post explaining his decision:

An article came out last night highlighting a new possible strategy for the House GOP Leadership to push through immigration reform. The article was the first I’d heard of this plan and mentions possibly borrowing language from a stand-alone military service bill that I’d supported in concept, and sneaking parts of it into the upcoming NDAA bill. I have a problem with this strategy for several reasons:

1) I’ve never been okay with Nancy Pelosi, the House GOP Leadership, or anyone else pulling a fast one on the American people by trying to sneak unrelated language into a larger bill. It’s not transparent, and it’s exactly why Americans don’t trust Washington.

2) Those of you who follow my votes know that I’ve always had concerns with these NDAA bills because of individual liberty conflicts involving indefinite detention. There’s enough bad stuff to worry about in the NDAA without adding more problems.

3) I have always been, and remain completely opposed to the idea of amnesty, that we should simply wipe the slate clean for those who broke our laws and our trust. My position continues to be that we must first secure the border and enforce our immigration laws, and not do that as part of some large comprehensive bill. We have to control who comes into our country and that can only happen by securing the border and addressing the massive amount of visa overstays first.

I was willing to have a conversation about the possibility of allowing some of the children who came here with their parents illegally to earn citizenship through military service. But that conversation should have been debated as part of a stand-alone bill that could not be conferenced with a broader bill, and then even only after we had made progress on enforcing our current immigration laws.

I will not allow Washington to pull their sneaky tricks on the public, so I am withdrawing the conditional support I had for the stand-alone military service legislation and have warned leadership that if they attempt to add this language as an amendment to the NDAA that I will vote against the entire bill for that reason alone. Hope this clears things up, and makes it perfectly clear where I stand.