"This is not a dictatorship. This is a democracy," Engel said at a candidate forum. "We shouldn't have one person, from high, even though she's a colleague of mine, think that she can anoint whoever's elected."
Engel's comments touched on simmering discontent in a party in which longtime lawmakers have faced several progressive primary challenges from candidates backed by Ocasio-Cortez.
On Wednesday, Ocasio-Cortez backed middle school principal Jamaal Bowman in his challenge against Engel, who was first elected to Congress in 1988.
“Once again, she has abandoned her colleagues in Congress and supported an outsider," a Democratic source previously told Fox News. "Sadly, the people she supports often lose. That might be different here, but it has little to do with her. She came in in the ninth inning.”
Ocasio-Cortez’s support for Bowman puts her in direct opposition to House Speaker Nancy Pelosi, who as a party leader backs incumbents when they face primary foes.
“He does a great job for New York and I wish him well on his election, as I wish her well on her election,” Pelosi said on Thursday when asked about Ocasio-Cortez’s opposition to Engel.
“This moment requires renewed and revitalized leadership across the country AND at the ballot box,” Ocasio-Cortez, 30, tweeted as she lent her support to Bowman, who is black.
Her announcement came during the second week of nationwide protests following the death of George Floyd.
The primary to represent New York's heavily Democratic 16th congressional district will be held June 23. Ocasio-Cortez is also facing a primary challenge in the nearby 14th district.
Fox News' Marisa Schultz and the Associated Press contributed to this report.