The American Civil Liberties Union (ACLU) has sent out a mailer in South Carolina questioning former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE's stances on civil rights issues after the group said the candidate did not answer its questions.

The ACLU is also running digital ads in the state targeting the stances of both Biden and Sen. Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-Minn.), who the group said also did not answer its questions.

"ACLU asked Joe Biden to answer a few questions about civil rights and civil liberties. Seven candidates who qualified for the next debate submitted responses...but Joe Biden hasn't," said the mailer, obtained by The Hill.

"Does Joe Biden support rights for all?" it said.

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ACLU Political Director Ronnie Newman told The Hill in a Wednesday interview that the mailer landed Friday and that a second similar mailer also targeting Biden will land Thursday or Friday of this week.

The second mailer will ask "Where is Joe Biden on civil rights? On whether voting is a fundamental right? On whether or criminal justice system is broken and unfair?"

Newman said in the interview that the mailers and ads are meant to put pressure on the candidates to answer its questions, but are not based on their records or stances on the issues.

"This initial phase that we're in is purely focused on info collection," he said. "What we are looking for is for each and every candidate regardless of party to let us know where they stand."

The Hill has reached out to the Biden and Klobuchar campaigns for comment.

The action is part of the ACLU's first "Rights for All" voter engagement campaign that was launched earlier this year.

Biden, who has consistently polled as the Democratic front-runner, has also faced more pointed questions regarding his record on civil rights issues. During the first Democratic debate, he clashed with Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE over his 1970s position on busing black students into majority white schools. He has also faced criticism over a 1994 crime bill he helped author. He has said that the bill did not lead to mass incarceration, but others, like Harris, have said that it did.

Biden's campaign does have a criminal justice plan on its website, the goals of which include reducing the number of people who are incarcerated and eliminating race, income and gender disparities in the justice system.

Biden and Klobuchar are among the 20 people running for the 2020 Democratic presidential nomination. Both have qualified for the September debate.