The actor, 57, took to Twitter to share a photo of Heigl, 41, accusing the actress, with whom he starred on the early seasons of the ABC series, of previously declaring he should never be allowed to speak publicly
"This woman once proclaimed that I should 'never' be allowed to speak publicly again," he wrote. "The world agreed with her proclamation back then and protested for my job and my head in 65 languages. I wish I was on Twitter in 2007, because I will NEVER stop exercising my free speech."
A fan responded to Washington, who portrayed Dr. Preston Burke, saying, "What speaks to your strength are the lessons you have learned and how you have moved on in a positive way."
"I've learned that all money ain't good money and no amount of money can replace your dignity and integrity," he responded. "Some call it living by your principles."
Heigl, who played Isobel Stevens on the show, previously alleged Washington had made a homophobic slur towards their co-star T.R. Knight on set.
He later addressed the claim at the 2007 Golden Globe Awards, prompting Heigl to reportedly declare that Washington "needs to just not speak in public." Within months, ABC announced the actor would not be returning to the show for its next season.
He is said to have penned an official apology and also shot a PSA for gay rights supporters, GLAAD, while showrunner Shonda Rhimes appeared to take aim at Heigl while discussing her show "Scandal" in 2014.
"There are no Heigls in this situation," she told The Hollywood Reporter. "I don't put up with bulls**t or nasty people. I don't have time for it."