Breitbart has been pressed since 2016 by a Twitter campaign called “Sleeping Giants,” which urges its more than 200,000 Twitter followers to ask companies to drop their ads from the right-wing news site.

In what Fast Company called an “uncannily effective” push, Sleeping Giants focused on companies that bought “programmatic” ads through ad services like Google and might not have even realized that their ads were on Breitbart.

Hundreds of companies ended up “blacklisting” Breitbart from running their ads. Over a two-month period in 2017, Breitbart lost 90 percent of its advertisers.

Now Breitbart is preparing to push back in court.

In a Wednesday letter, Breitbart’s attorney told Sleeping Giants to start preserving documents about their group’s contacts with a wide range of groups ahead of a potential lawsuit, including advertisers, social networks, reporters, academics, liberal activists, Media Matters, and all “persons or organizations” supported by billionaire Democratic financier George Soros.

In the letter, Breitbart’s attorney claims that Sleeping Giants is a “smear campaign” organized with a “secret network of supporters.” The letter lists a number of potential options for a civil lawsuit against Sleeping Giants, including tortious interference and fraud.

“Sleeping Giants is a highly-orchestrated, partisan campaign whose organizers have proven willing to use deception and harassment to achieve their goals,” the letter reads.

The letter claims that Sleeping Giants unfairly labeled Breitbart as anti-Semitic. Former Breitbart chief Steve Bannon has described the site as a “platform for the alt-right.”

In a statement, Sleeping Giants’ founder Matt Rivitz, a freelance copywriter, said the campaign was merely pointing out to advertisers that their ads were running on Breitbart.

“Sleeping Giants lets advertisers know that their ads are appearing on a website that publishes articles with titles like, ‘There’s No Hiring Bias Against Women in Tech, They Just Suck At Interviews,’” Rivitz said. “Breitbart can say whatever they want, and that's what makes this country great, but it doesn't mean they need to get paid for it by an advertiser who didn't know their ads were on the site.”

Breitbart, which published the letter on its site on Wednesday, didn’t respond to a request for comment.

Breitbart wants Sleeping Giants to preserve any communications with a long list of individuals and groups, including Facebook, Twitter, Google, Amazon, and all of the group’s contacts with reporters, advertisers, or ad networks.