The matchup is not yet official, but sources confirmed the plans to ESPN. The UFC 225 pay-per-view takes place at United Center. BJPenn.com first reported the rematch.
Whittaker (19-4) requested the June 9 date on social media last month. The Australia-based champion defeated Romero via unanimous decision to win the interim middleweight title at UFC 213 last summer. Whittaker was promoted to the undisputed titleholder after Georges St-Pierre vacated the belt last year.
He was supposed to make his first defense against Luke Rockhold at UFC 221 in Perth, Australia, but was forced off the card with multiple injuries.
Romero (13-2) ended up taking Whittaker's place on that card and defeated Rockhold by third-round TKO. A former Olympic wrestler for Cuba, Romero is 9-1 in the UFC. He trains out of Miami.
Whittaker is also scheduled to represent Australia in the 2018 Commonwealth Games next month. He will be the first active UFC champion to do so.