Rep. Kevin McCarthy of California, the Republican whip, posed with the birthday girl and her uncle, Rep. Fred Upton, R-Mich., in the shot he put on Instagram, the New York Daily News reported. The location of the party was not revealed.
Upton, who appeared in a bikini on the cover of Sports Illustrated in January, was wearing a sleeveless black dress that showed no cleavage.
Upton's 21st birthday was Monday. She sent out thanks via Twitter: "My friends and family are the best!! Thank you everyone for your birthday wishes."
Her uncle told Fox News in 2012 Upton is a "great gal."