"I am so touched by your support for our show," Sagal, 67, wrote. "As a cast and great crew and the amazingly talented @kristavernoff have just begun to gel and find our footing, the plug has been pulled, and I feel you and hear your disappointment. I wholeheartedly stand with you. "
The actress wrote that "the abrupt announcement that there would be no season 2 based on the response from four airings came as a shock and a heartbreak."
Sagal argued that sometimes when it comes to shows like Rebel, "Things take time to catch on," and basing a judgement on four episodes isn't fair.
"Rebel tells the story of a woman who speaks up for what is right, the show has heart and purpose, funny and tears, and we, the cast, are all scratching our heads at the reversal of support from ABC," she continued."
"As Rebel would say, fight for what you want, make people listen, and in this case, if our show can find another, more suitable place to land, we will do the happy dance," she continued. "If not, we gave it our all and made our voices heard, which is the message behind Rebel! Always Speak Up!!"
Sagal encouraged fans to share the post and sign a fan petition calling for ABC to reverse their decision to end the series.
The show, which was created by Krista Vernoff, still has five episodes set to air before the season comes to an end.
ET spoke with Sagal -- and her Rebel co-star Andy Garcia -- back in March, and she opened up about why she took on the role, which she was was "too good to pass up."
"I was not necessarily looking for another hour-long television show to do because of the schedule, [but] I couldn't say no," Sagal shared, adding that her character has many qualities that interesting to her as an actress. "She's very unapologetic. In fact she's rude and crass, and that's fun."
For more on Rebel -- which airs Thursdays at 10 p.m. ET/PT on ABC -- check out the video below.