"Robert Becker, who directed Sanders" Iowa campaign and served as deputy national field director, is alleged to have approached a female staffer at a Philadelphia bar where members of the campaign had gathered, Politico reports.
Becker, 50, has denied the allegations.More news: General Motors Oshawa plant workers stage sit-down strike
More than two dozen former staffers recently sent a letter to Sanders and his aides, seeking a meeting regarding the "sexual violence and harassment on the 2016 campaign" ahead of another bid for the presidency.
"Candidates who allow people like Robert Becker to lead their organizations shouldn't earn the highest office in our government", she said in a statement.
"It just really sucks, because no one ever held him accountable". This can't happen in 2020.
She said she felt compelled to speak out after Mr Becker travelled to SC in December on a trip to recruit future campaign workers for Mr Sanders. The Vermont senator also said he wasn't aware of a reported $30,000 settlement Becker was named in to resolve a discrimination claim against his 2016 campaign.More news: South African teacher suspended over seating students by race
Becker traveled to SC - the first-in-the-South primary state - in December for meetings with former Sanders campaign staffers, CNBC previously reported.
The woman did not report the incident at the time since the campaign was finished but has come forward now as Becker has been involved with potential 2020 groundwork. The alleged assault, he wrote, is "at odds with my recollection of a late evening filled with many hugs and kisses and tears and conversations about what's next".
But Becker, who is not on Sanders' payroll, has been calling potential staffers and traveling to early primary states over the past several months in moves seen as preparing for a 2020 campaign. "In terms of addressing the needs that I'm hearing from them now, that women felt disrespected, that there was sexual harassment, which was not dealt with as effectively as possible". The New York Times reported last week that a Latino outreach strategist for the campaign complained to a supervisor that she had been harassed by a campaign surrogate. But Jeff Weaver, who ran Sanders' 2016 campaign, stressed then that Becker was not doing so in an official capacity as he "doesn't work for the campaign because there is no campaign". However, to the women who were allegedly harassed, he said that "what they experienced was absolutely unacceptable and certainly not what a progressive campaign, or any campaign, should be about".
Weaver is a longtime Sanders ally who served as chief of staff during Sanders' tenure in the U.S. House and later in the Senate.More news: Woman in vegetative state who gave birth was 'raped several times'