The newly minted Republican nominee for North Dakota's open U.S. Senate seat is facing criticism by his Democratic opponent for voting against cutting the congressional mail budget.

Rep. Rick Berg, who easily captured the nomination Tuesday night, voted last week against an amendment to cut the federal budget for official congressional mail by 10 percent. The measure, offered on the House floor by Rep. Chellie Pingree (D-Maine), failed 309-101, with Berg joining 229 other Republicans and 79 Democrats in voting against it.

Berg's vote comes amid reports that he has spent 15 percent of his official budget on direct mail pieces to North Dakota residents. The Associated Press reported in March that Berg spent just under $190,000 -- or 15 percent of his $1.24 million federal allotment -- on the mailers. Berg's spokeswoman at the time, Alee Lockman, told AP that the mailers were official business and not a campaign effort.

"He does take communication with constituents very, very seriously," Lockman said at the time. "He is always looking for different ways to reach out to people."

The campaign for Heidi Heitkamp, a former state attorney general and the state's Democratic Senate nominee, slammed Berg for voting against the amendment. The North Dakota Senate is one of the nation's most competitive, with the latest poll showing that Heitkamp has a one-point lead.

“Rick Berg doubled down on government waste and voted to preserve the taxpayer funded mailers he used to advance his political career,” Brandon Lorenz, a spokesman for Heitkamp, said Tuesday. "Berg's vote to preserve the government waste he uses for political gain is just like his self-interested votes to raise his own pay, block raising the minimum wage and gut crop insurance for North Dakota farmers. This is just the latest example of him using his position in Washington to advance his own interests instead of doing what’s best for North Dakota."

Berg's congressional spokesman, Chris Pack, did not return multiple requests for comment about Berg's decision to vote against the amendment. Berg's campaign spokesman, Chris Van Guilder, referred all questions to Pack, saying it was an official matter.

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