RALEIGH, N.C. (AP/WNCN) — Allegations of flagrant absentee ballot fraud in a North Carolina district have thrown the Election Day results of one of the nation’s last unresolved midterm congressional races into question.

Unofficial ballot totals showed Republican Mark Harris ahead of Democrat Dan McCready by 905 votes in the 9th Congressional District. But the state elections board refused to certify the results last week in view of “claims of numerous irregularities and concerted fraudulent activities” involving mail-in ballots in the district.

The elections board has subpoenaed documents from the Harris campaign, a campaign attorney confirmed Tuesday. Investigators seem to be concentrating on activities linked to a longtime political operative from Bladen County, where allegations about mail-in absentee ballots also surfaced two years ago during a tight election for governor.

In affidavits offered by the state Democratic Party, voters described a woman coming to their homes to collect their absentee ballots, whether or not they had been completed properly. State law bars this kind of “harvesting” of absentee ballots, which must be submitted by mail or in person by the voter or a close family member.

If the allegations are accurate, “this is the biggest absentee fraud in a generation or two in North Carolina,” said Gerry Cohen, an election law expert and former longtime legislative staff attorney. “North Carolina has a long history of this kind of thing, particularly in rural areas.”

Bladen County was the only county in the district where Harris won a majority of the mail-in ballots, according to unofficial election data. Bladen and Robeson County — where officials also have requested information — had the district’s highest percentages of unreturned mail-in absentee ballots. The total number of unreturned ballots exceeded the current margin.

The district attorney in Raleigh announced this week that she’s been investigating potential Bladen County “voting irregularities” since last January. The investigation that began with claims from 2016 has now spread to this year’s primary and general elections, Wake County DA Lorrin Freeman said in an interview.

Freeman said she was investigating in part because of comments made by McCrae Dowless of Bladen County during a State Board of Elections hearing in December 2016. Dowless worked as a contractor for Harris’ chief strategist in the campaign, Harris campaign lawyer John Branch confirmed Tuesday.

Dowless, who served prison time in 1995 for felony fraud and was convicted of felony perjury in 1992, has worked on get-out-the-vote efforts for various local and legislative candidates through the years. Dowless put his name on an elections protest, backed at the time by the campaign of then-GOP Gov. Pat McCrory, that alleged a “massive scheme” by a local political group to run an “absentee ballot mill” to improperly submit votes for a write-in candidate for a position Dowless was seeking.

But the board peppered Dowless with questions about his own absentee ballot activities. Dowless acknowledged he hired people in 2016 to urge voters to turn in absentee ballot request forms, which is legal. In sworn testimony, Dowless said he never handled or filled out the actual ballots. The board dismissed Dowless’ protest but sent all of its evidence to local and federal prosecutors.

Visited by a reporter Tuesday at his Bladenboro home, Dowless declined to comment. He said the voice on the speaker phone in his hand was that of an attorney advising he decline to describe his election activities.

The elections board has said it will hold a hearing on the allegations on or before Dec. 21. Board members can call for a new election if they find enough problems that could have altered the outcome or cast doubts on the election’s fairness. An election would take place well after the new session of Congress convenes Jan. 3, likely creating a temporary vacancy.

Republican leaders say Harris, a Southern Baptist minister, should be certified the winner, saying no evidence has been made public that show he didn’t get the most lawful votes.

“The campaign was not aware of any illegal conduct in connection with the 9th District race,” Branch said in a statement.

Although Democrats won enough House seats nationally to take back the chamber come January, the 9th is gaining attention in part because a Republican has held the seat continuously since 1963. Democrats had hoped McCready, an Iraq War veteran, would end the streak, especially after Harris edged U.S. Rep. Robert Pittenger in the May GOP primary.

“The bottom line is this: If there proves to be fraud, then there must be consequences,” said U.S. Rep. Cheri Bustos, D-Ill., who leads the Democratic Congressional Campaign Committee.

Pittenger narrowly lost to Harris last May in part because of Harris’ strong showing in Bladen County, where he received 96 percent of the mail-in absentee votes. Pittenger said he sat down briefly in 2016 with Dowless, who pitched him a plan to work for his campaign and sign up absentee voters.

“I said no thank you,” Pittenger told The Associated Press in a phone interview. “I just didn’t feel comfortable.”