In a rapid and dramatic policy shift, Confederate flag imagery could be allowed to remain displayed on graves on federal land in some circumstances under a Republican-sponsored amendment that will be voted on in the House on Thursday.

Ken Calvert, R-Calif., announced the unexpected change of plans Wednesday evening as floor debate wrapped up on the fiscal 2016 Interior-Environment spending bill (HR 2822). The Interior-Environment Appropriations chairman and floor manager set a roll call vote on the Confederate flag amendment for Thursday, when lawmakers are scheduled to vote on final passage of the $30.2 billion measure.

The move came just 24 hours after the House adopted by voice vote a trio of Democratic amendments that would restrict Confederate flag imagery on federal land. That was the House’s first move in a national debate over the flag’s place in American society, a discussion that was spurred by fatal, racially motivated shootings at a black church in South Carolina last month.

The GOP amendment was opposed by Minnesota Rep. Betty McCollum, ranking Democrat on the Interior-Environment Appropriations Subcommittee, who was audibly shaken while speaking on the floor and said she “cannot hide my surprise and my outrage.”

“After the murder of nine black parishioners, I never thought that the U.S. House of Representatives would join those who would want to see this flag flown by passing an amendment to ensure” the continued flying of the Confederate flag, McCollum said.

The Republican amendment would effectively undo two of Democratic amendments adopted on the floor Wednesday; no members spoke in opposition at the time. Those amendments would block funding from being used to decorate a grave in a federal cemetery with the flag and bar the National Park Service from using funds to contract with gift shops that sell merchandise with Confederate flag imagery.

Calvert’s announcement of the GOP amendment came after he had spoken on the House floor for nearly half an hour. The chamber had seemingly completed work for the day on the spending bill. He spoke about several other provisions in the underlying bill, moving to “strike the last word” — a procedural move to get more time to continue his speech — until an aide interrupted him with an amendment to offer.

Calvert kept his remarks on his provision short.

“This amendment will codify existing National Park Service policy and directives with regard to the decoration of cemeteries and concession stands,” he said. “I urge adoption of my amendment.”

McCollum in a statement said that the amendment was apparently needed to get the overall bill passed. “For House Republicans it appears the cost of getting the votes to pass this terrible Interior-Environment Appropriations bill is to literally wrap themselves in this banner of racism,” McCollum said. “This bill is already a polluter’s dream, now the majority wants to make the bill truly toxic with this amendment.”

Republicans were unlikely to get much — if any — Democratic support on the historically contentious Interior-Environment spending measure, making party unity key to passage.

Spokesmen for Speaker John A. Boehner, R-Ohio, and House Majority Leader Kevin McCarthy, R-Calif., did not immediately respond to requests for comment.

Nita M. Lowey of New York, the top Democrat on the House Appropriations Committee, issued a statement Wednesday evening urging lawmakers to “reject this disgraceful gambit.”

“The Calvert amendment would shamefully challenge the emerging national consensus that government must not countenance such a symbol of hatred and intolerance,” Lowey said in a statement.

A GOP aide said the Calvert amendment would effectively codify a recent policy memo from National Park Service Director Jonathan B. Jarvis, which allows for Confederate battle flags to be displayed only in limited circumstances, such as to temporarily adorn the graves of Civil War veterans on federal property in states that celebrate Confederate Memorial Day, a holiday in some Southern states.

The staffer said the amendment would also codify Jarvis’ request that the facilities voluntarily withdraw items depicting the flag as a “standalone feature.”

Steve Israel, a member of the Interior-Environment spending panel, said Democrats would “refuse to allow [Republicans’] despicable actions to go unnoticed.”

“As our country struggles, in the wake of tragedy, to rid itself of the painful symbol of hate that the Confederate flag represents, House Republicans are forcing a late-night, backdoor strategy to allow its continued use,” the New York Democrat said.

Another flag-related amendment that was previously adopted to the bill would be left in place, according to the aide. That provision, sponsored by Hakeem Jeffries, D-N.Y., would block funding for NPS to purchase or display a Confederate flag on park property except to provide historical context.

Ryan McCrimmon and Emma Dumain contributed to this report.