North Carolina Republicans set off pandemonium in the state's House of Representatives on Wednesday by passing a controversial budget while some Democrats were absent during a 9/11 memorial ceremony.

The Republicans overrode Democratic Gov. Roy Cooper's veto of the state budget with a 55-9 vote.

The News & Observer reported that one Democratic member was attending a 9/11 memorial ceremony, as was Cooper.

House Republicans have said Democrats were merely absent from the floor to secretly redraw maps of political districts in violation of a court order, though Democrats have denied they broke any rules.

Democratic leaders accused Republicans of trickery, saying that Republicans had assured them there would be no formal votes on the morning of the 18th anniversary of the 9/11 terrorist attacks.

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Republicans in the North Carolina House of Representatives stunned their Democratic colleagues on Wednesday by holding a surprise vote and passing a controversial budget while many of its members were absent.

The Republicans overrode Democratic Gov. Roy Cooper's veto of the state budget with a 55-9 vote, while colleagues were absent from the floor during a 9/11 memorial ceremony.

To override the governor's veto, the Republicans needed to secure a three-fifths majority vote among those present. Local news outlets reported that Republicans in the state had been trying for months to override Cooper's veto and seized an opportunity on a morning typically set aside to honor the 2,977 people killed in the 9/11 attacks 18 years ago.

The News & Observer reported that one Democratic member was attending a 9/11 memorial ceremony at the time of the vote, as was Cooper. House Republicans have since said Democrats were merely absent from the floor to secretly redraw maps of political districts in violation of a court order, though Democrats have denied they were breaking any rules.

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Democrats also said they were tricked by Republicans into believing there would be no vote in their absence. House Minority Leader Darren Jackson said at a press conference that the House rules committee chairman told him the chamber would hold no recorded votes on the floor until 1 p.m.

'You are making a mockery of this process'

Cooper told reporters in a press conference Wednesday that Republicans' move was an "assault on our democracy."

"There is no question about it," he said.

He said voters should be "outraged that this Republican leadership would orchestrate such deception, such trickery in order to get their way."

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Reports quickly surfaced on social media of chaos on the House floor as Democrats shouted at their Republican colleagues about the move. In a video, Rep. Deb Butler, a Democrat who was present for the vote, could be heard condemning the Republican House Speaker Tim Moore.

"How dare you do this, Mr. Speaker," Butler said. "Mr. Speaker, you are making a mockery of this process. You are deceiving all of North Carolina. Your leadership is an embarrassment to the history of this great state."

Butler later told reporters she was threatened with arrest, though the House's sergeant at arms denied that, the NBC affiliate WRAL reported.

Editor's note: This story has been updated to clarify that Republicans have said many Democrats were absent from the floor to secretly redraw political maps, while Democrats have denied they were doing anything secretive.