The Motion Picture Association (MPA) in the US has sent Meta a cease-and-desist letter over its use of "PG-13" when referring to content moderation on Instagram.
In October, the social media giant announced that teenagers using its platform would now only see content that abides by a PG-13 cinema rating.
Now, it has been told to "immediately and permanently" stop using the rating, with the MPA accusing Meta of being "highly misleading".
The MPA's film ratings, which range from G (suitable for all ages) to NC-17 (18+), are decided on by parents who watch the films and then evaluate them to come up with a rating.
"Meta's attempts to restrict teen content literally cannot be 'guided by' or 'aligned with' the MPA's PG-13 movie rating because Meta does not follow this curated process," said the association's letter, seen by Sky News.
"Instead, Meta's content restrictions appear to rely heavily on artificial intelligence or other automated technology measures."
The MPA is a US trade body that describes itself on its website as the "leading advocate of the global film, television, and streaming industry".
Naresh Kilaru, a lawyer for the MPA, said in the 28 October letter to Meta: "The MPA has worked for decades to earn the public's trust in its rating system."
"Any dissatisfaction with Meta's automated classification will inevitably cause the public to question the integrity of the MPA's rating system," Mr Kilaru said.
Read more from Sky News:
How the world's richest man is boosting the British right
Tech giants warn Reeves of IPO 'flight risk' over budget
The letter to Jennifer Newstead, Meta's chief legal officer, asked Meta to immediately disassociate Instagram's Teen Accounts and AI tools from the MPA rating system and to refrain from any use of the PG-13 mark.
It asked for a resolution by 3 November. On 6 November, however, Sky News checked and was still presented with a message on Instagram saying: "Instagram Teen Accounts will be guided by 13+ movie ratings."
Meta told Sky News that parents say they want to "better understand" what their teenagers are seeing on Instagram.
"To make things simpler for them, we updated our teen content policies to be closer to PG-13 movie standards - which parents already know," said a Meta spokesperson.
"We know social media isn't the same as movies, but we made this change to support parents, and we hope to work with the MPA to continue bringing families this clarity."
(c) Sky News 2025: Meta told to stop using PG-13 film-style ratings over Instagram content
One of two prisoners mistakenly released hands himself in
Man who killed 'Good Samaritan' by running him over as he helped woman lying in street is jailed
Andrew's prince title and HRH style formally removed by the King
Mexico's President Claudia Sheinbaum presses charges after groping incident
How Andrew allegations unfolded and his titles were lost
Lammy defends failing to reveal another prisoner had been mistakenly released
What we know so far about the prisoners freed by mistake
Nancy Pelosi, the first woman in Speaker's office, to stand down after 40 years in US Congress