WATCH: Conservative groups lobby against border tax on Capitol Hill

Conservative groups are pushing against the border-adjustment tax, a key provision in the House Republicans' tax plan.

"Unfortunately we've seen a number of politicians, including on the Republican side, pushing this [tax]," Sean Lansing from Americans for Prosperity told The Hill. "We think it's just a massive $1.2 trillion tax hike on American consumers."

Under the border-adjustment tax, imports would be subjected to a 20 percent tax, while exports would be exempted.

Rep. Pete Roskam (R-Ill.) told The Hill the tax would level the playing field for American companies, which he says are being taken advantage of.

"We're the only large economy in the world that doesn't adjust taxes at the border. One-hundred and sixty countries adjust at their borders. Currencies will adjust over time, and I think we'll be in a very good position if we do this."

House lawmakers haven't settled on a border adjustment tax, but retailers are pressing forward with lobbying efforts to prevent a border-adjustment tax from becoming part of tax reform package.