The American Accountability Foundation is requesting an ethics investigation into whether New York Democratic Rep. Alexandria Ocasio-Cortez accepted an "impermissible gift" by attending the Met Gala in New York City.
According to media reports, individual tickets cost about $30,000-$35,000.
New York Democratic Rep. Carolyn Maloney also attended the star-studded event over the weekend.
The AAF, a conservative organization, formally filed the complaint with the Office of Congressional Ethics.
"Specifically, we believe Representative Ocasio-Cortez has violated clause 5 of Rule XXV of the Rules of the House of Representatives (commonly known as the Gift Rule) by accepting admission to the Met Gala, an event whose per seat costs is reported to range from $35,000 to $50,000, without having a permissible exemption to allow the acceptance of the lavish gift," wrote AAF Founder Thomas H. Jones. "If Representative [Ocasio-Cortez] has used campaign funds to pay for this ticket, she has also violated FEC prohibitions on campaign funds being used for entertainment purposes.
"Without prompt investigation and enforcement of Congressional Rules, the American people are likely to lose faith in the ability of Congress to police its members."
The Office of Congressional Ethics did not return a request for comment before publication. The House Ethics Committee declined to comment.
Ocasio-Cortez responded to critics of her Met Gala appearance, where she wore a dress that said, "TAX THE RICH."
"And before haters get wild flying off the handle, New York elected officials are routinely invited to and attend the Met due to our responsibilities in overseeing and supporting the city's cultural institutions for the public," she tweeted. "I was one of several in attendance in this evening."
"I thought about the criticism I'd get," she said in response to a question on her Instagram story, "but honestly I and my body have been so heavily and relentlessly policed from all corners politically since the moment I won my election that it's kind of become expected and normalised to me."