"So I think I'm gonna have to make that hashtag a thing," she wrote.
"I will be calling [out] harmful messaging from brands or companies that perpetuate a society that not only enables but praises disordered eating".
Lovato has spoken in the past about her own struggles with disordered eating, revealing she first sought treatment for bulimia at 18 and said that her relationship with food was a contributing factor to her 2018 overdose.
"I didn't control any of my life at that period of time," Lovato recently told CBS.
"Every time I was in a hotel room my phone was taken out of the room so I couldn't order room service."
The company responded in a direct message to Lovato, denying they were "diet vultures" and she shared the exchange with her fans.
In her reply to The Bigg Chill, Lovato said "the whole experience was triggering and awful".
"You can find a way to provide an inviting environment for all people with different needs. Including eating disorders - one of the deadliest mental illnesses only second to opioid overdoses," she claimed.
"Don't make excuses, just do better"
When The Bigg Chill said its marketing of sugar-free and vegan options are designed to cater to diabetic clients and others with specific needs, Lovato said the marketing could be improved and was "not super clear".
Lovato has returned to the headlines recently after taking time out following a near-fatal drug overdose in 2018.
The Confident hitmaker was rushed to hospital after the terrifying incident and has said she "didn't know" if she'd ever sing again after her near-fatal overdose.
Despite her battles with addiction, Lovato has taken a "California Sober" approach to her recovering, meaning she drinks alcohol and smokes marijuana in moderation, but she insisted what is right for her wouldn't necessarily be right for others with her background.
She said recently: "I've learned that it doesn't work for me to say that I'm never going to do this again ... I know I'm done with the stuff that's going to kill me, right? Telling myself that I can never have a drink or smoke marijuana, I feel like that's setting myself up for failure because I am such a black-and-white thinker."
- Additional reporting, BANG! Showbiz
