Rep. Alexandria Ocasio-Cortez (D-NY) endorsed Marie Newman, the progressive House candidate running a primary campaign against conservative Rep. Dan Lipinski (D-IL), on Tuesday.

In her first endorsement of an incumbent Democrat’s challenger, Ocasio-Cortez praised Newman as a “grassroots fighter for working families” in Illinois’ 3rd District.

“To me, choosing to support is about more than just policy,” the New York Democrat tweeted. “It’s also about who puts in the WORK. Are they wearing out their shoes?”

“Marie is. Her supporters are,” she continued. “Let’s knock doors & join them.”

Marie Newman (@Marie4Congress) is a grassroots fighter for working families in #IL03. To me, choosing to support is about more than just policy. It’s also about who puts in the WORK. Are they wearing out their shoes? Marie is. Her supporters are. Let’s knock doors & join them. https://t.co/jjSy4Anc14 — Alexandria Ocasio-Cortez (@AOC) September 17, 2019

Newman said she was “thrilled” to receive the endorsement in an emailed statement to TPM.

“Her unwavering dedication to fighting for social, climate and economic justice is a true inspiration,” she said. “I look forward to working with Congresswoman Ocasio-Cortez and other Progressive Caucus members in Congress to fight for policies that make life safer and more affordable for people in my District.”

Lipinski, a conservative Democrat known for his anti-abortion and anti-LGBTQ views, derided Ocasio-Cortez’s endorsement, saying in a statement to NBC News reporter Alex Seitz-Wald that his constituents “do not want to be represented by a fifth member of the ‘Squad.'”

“The Democratic Party–and our country– cannot afford an obstructionist ‘Tea Party of the Left’ when we need to focus on wining [sic] this next election and passing policies that will truly help working families and all who are struggling in America today,” he said.

The Democratic Congressional Campaign Committee, which is helping to raise funds for Lipinski’s campaign, did not respond to request for comment.

2020 presidential candidate Sen. Elizabeth Warren (D-MA) also endorsed Newman last week, saying that Illinoisans “deserve a leader with an unwavering commitment to fighting for women’s access to reproductive health care.”