NEW YORK (Reuters) - A recount will begin on Tuesday in the Democratic primary race for district attorney in the New York City borough of Queens, a contest that drew national attention, an official said on Friday.

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Tiffany Caban, a progressive Democrat endorsed by U.S. Representative Alexandria Ocasio-Cortez, declared victory last week, but her rival, Melinda Katz, did not concede.

A win for the 31-year-old Caban, a political newcomer, would mark a fresh signal of the growing power of the Democratic Party’s progressive wing ahead of the 2020 presidential election.

Caban saw her 1,100-vote lead vanish on Wednesday as 3,400 absentee ballots pushed Katz, an established centrist who serves as Queens borough president, ahead by 20 votes.

Under New York City Board of Elections policy, a recount is mandatory when the victory margin is under 0.5 percentage point, said board spokeswoman Valerie Vazquez-Diaz. The date for the recount to begin was released on Friday.

The tight margin also sparked accusations that election officials improperly dismissed more than 2,000 affidavit ballots before the paper ballots were counted.

Lawyers for both candidates presented affidavit ballots to board officials on Friday and argued why certain ones should or should not be counted, according to Vazquez-Diaz.

With Democrats outnumbering Republicans in Queens, the winner of the Democratic primary is expected to easily defeat a Republican opponent in November’s national election.

“With a full recount coming up, there’s more work to be done. Help us make sure every valid vote is counted!” Caban wrote on Twitter on Friday.

“We’re going to be in court and going to present evidence that there are still many more ballots that should be opened that should enable us to win,” said Jerry Goldfeder, a veteran election lawyer representing Caban.

Officials from the Katz campaign also reiterated their confidence in the upcoming recount.

“Our position has been, when we were behind 1,100 votes, that every vote should count. And our position today remains the same,” Matthew Rey, a partner at Redhorse Strategies, a political consulting group representing Katz, said in a statement.