CHICAGO (AP) — Massachusetts Sen. Elizabeth Warren joined former Vice President Joe Biden on Wednesday in a presidential campaign pledge to avoid the use of fake news, manipulated images or online misinformation.

The declaration signals that viral misinformation is becoming a growing concern for the campaigns as the Democratic primary season nears. Both Biden and Warren have been victims of online viral smear campaigns built on trending hashtags, heavily edited video and memes.

“We need more candidates stepping in and speaking against disinformation,” said Kanishk Karan, a misinformation researcher at the Atlantic Council, a Washington, D.C.-based think tank. “The discussion, by and large, is coming from the people who have experienced this sort of disinformation effort against their candidacy – and that’s an important point: the ones who’ve experienced this sort of attack against their reputation are standing up for it.”

Earlier this month, for example, social media users flooded Twitter with snake images and the term #NeverWarren to attack the candidate during a spat with fellow Democratic presidential candidate Sen. Bernie Sanders. In some cases, hashtags were used to spread misinformation, with Twitter users accusing her campaign of fabricating a mean-spirited text message from a Sanders campaign volunteer. His campaign later confirmed to The Associated Press that the text was sent by a rogue Sanders volunteer, who was booted from the effort.

Meanwhile, a video of Biden was selectively edited just this month and used on social media to wrongly claim he made racist remarks. He has also been targeted with misinformation in recent months, with many Republicans falsely claiming that he pressured Ukraine to fire a top prosecutor who was investigating Burisma, the energy company his son worked for at the time. In fact, the investigation was dormant when Biden pressed for the firing.

Biden signed a pledge last year that he would not use doctored images and videos or fabricated information during the campaign.

Warren’s pledge released Wednesday is part of a regulation proposal she promised to implement if elected president. Warren has long been a critic of the tech companies that operate online platforms sometimes used to spread misinformation and once called for breaking up tech giants like Facebook and Google.

Her plan to fight digital disinformation appears to be the first of its kind among the presidential candidates.

President Donald Trump, who has been reluctant to acknowledge that Russia used online disinformation campaigns in an attempt to influence U.S. voters during the 2016 election, has been criticized for not safeguarding the presidential race from such attacks again this year.

Warren’s plan calls on the tech companies to label propaganda that was written or produced by state-funded media outlets or the government and to ban accounts that put out false information about voting rules, times and locations.

In a statement, Facebook said it agrees with Warren on the importance of combating disinformation and believes “there needs to be a more substantive partnership between government private industry to better secure our elections.”

One of Warren’s ideas quickly became a casualty of online misinformation Wednesday. Some Twitter users inaccurately suggested she plans to criminalize disinformation all together, calling it a violation of free speech rights.

Her plan is actually more specific, saying that she would push for civil and criminal penalties only for people who “knowingly” disseminate information that has the “explicit purpose of undermining the basic right to vote.”

Twitter users easily circulated misleading comments about her plan, in part, because it’s long and complicated, said Jennifer Grygiel, an assistant professor of communications at Syracuse University.

“Yes, it’s important for us to be talking about disinformation … (but) politicians need to figure out how to package their ideas into memes,” Grygiel said of Warren’s plan. “We need to distill these ideas down for the public. If she doesn’t package the narrative, somebody else will.”

And criminalizing misinformation could be tough, Karan said.

Many people on social media might unknowingly spread misinformation by sharing it with their friends in a Facebook post or retweeting it. But they didn’t necessarily create the misinformation.

“It’s really hard to expose the source of disinformation,” he said. “That could become a challenge.” ———

Associated Press writer Barbara Ortutay in San Francisco contributed to this report.

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