America’s film certification body, the MPAA, has announced changes to the way it rates films, in response to growing concern about the possible links between violent films and real-life shootings.

Under pressure from the White House to tighten the controls, the MPAA said it would give parents more information about why films have been awarded particular certificates. Films that might previously have received a PG-13 rating, with a brief, one-sentence explanation as to why, will now feature extensive descriptions, in large print, next to the ratings code.

The Vice President Joe Biden has met the heads of the MPAA and the National Association of Theatre Owners, or NATO, which represents cinemas, to discuss the issue and President Obama himself has called for a stricter rating system.

Conservative groups have accused the MPAA of relaxing the ratings, allowing younger children to see more violent films, because more ticket sales boost the profits of the studios, which together run the MPAA. Even NATO has urged Hollywood to make fewer R-rated films.

Groups representing parents been hoping that more films would end up with the highest R rating. They’ve described the new system as a “distinction without a difference.”