Senate Democrats will press conservative dark money group Judicial Crisis Network on Wednesday to release the names of its donors, after the group ran an ad campaign demanding 2020 Democrats release a secret “list” of liberal judicial nominees that doesn’t actually exist.

In late June, JCN spent $1.1 million running ads, including during the Democratic presidential debates in Miami, that called on Democrats, especially former Vice President Joe Biden, to release their lists of potential judicial nominees.

Now Senate Democrats are calling for JCN to practice some transparency of its own. In a letter obtained exclusively by The Daily Beast, Senate Minority Leader Chuck Schumer (NY), Sen. Sheldon Whitehouse (RI), and at least six co-signers, including 2020 hopeful Sen. Cory Booker (NJ), are demanding that the conservative group reveal who’s funding its multi-million dollar ad campaigns in favor of conservative judicial nominees like Supreme Court Justices Neil Gorsuch and Brett Kavanaugh.

“Over the last week, the Judicial Crisis Network began a $1.1 million ad campaign calling for greater transparency by progressive advocacy organizations in the judicial nominations process,” the letter reads. “Yet, despite your organization’s claimed commitment to transparency, JCN continues to conceal the identity of its donors. As we understand it, these donors have contributed tens of millions of dollars used to fund political advertising campaigns in support of nominees like Brett Kavanaugh and Neil Gorsuch.”

JCN policy director and chief counsel Carrie Severino didn’t respond to requests for comment.

Senate Democrats want JCN to release a wide range of information about its donors, and specifically ask about a $17.9 million donor who provided nearly all of the group’s funding in 2017.

In the letter, the Democrats ask for the names of every JCN donor who gave more than $10,000 and the total number of donors since 2017. They’re also seeking the number of small donations of less than $100 that the group has received, as well as what percentage of the dark money group’s funding comes from corporations.

“The American public deserves to know who is funding these attacks, and whether the same individuals are financing litigation before the Court that will ultimately be decided by the Justices and judges they helped to confirm,” the letter reads.

Along with Schumer and Booker, the letter’s other signatories include Sens. Sheldon Whitehouse (RI), Bob Menendez (NJ), Mazie Hirono (HI), Richard Blumenthal (CT), Jack Reed (RI), and Democratic Whip Dick Durbin (IL).

While Democrats are tying the letter to JCN’s push for a “list” supposedly held by Biden and other 2020 Democrats, it’s not clear the list that JCN wants actually exists.

The JCN ad campaign was premised on the idea that 2020 Democrats have a secret list of judicial nominees. That’s apparently a reference to “Building the Bench,” a progressive project led by liberal judicial group Alliance for Justice to find potential Democratic nominees.

But Nan Aron, the founder of Alliance for Justice, says the “list” that JCN ads are pressing Biden for doesn’t exist—at least not in a way that’s held by candidates. Instead, Aron told The Daily Beast that AFJ is evaluating potential judicial nominees for a future Democratic president.

“I’m not sure where Carrie Severino got the idea of a list,” Aron said. “We certainly have never produced lists for candidates or shared lists.”

Aron said the JCN ad campaign is proof that the liberal nominee effort has “hit a nerve” with Severino, even if the ads are premised on a nonexistent list.

“They’re very creative,” Aron said.