Fashion giants LVMH and Kering have announced they are banning the use of size zero models under a new "well-being charter" across all their brands.
The two groups, whose brands include Alexander McQueen, Stella McCartney, Gucci, Saint Laurent, Christopher Kane, Louis Vuitton and Dior, have committed to banning the casting of French size 32 for women - the equivalent of a US size zero or UK size four.
They will only work with models able to present a valid medical certificate "attesting to their good health and ability to work" and their brands must no longer hire models aged under 16 for shoots or shows representing adults.
The move will come into effect during the upcoming fashion weeks beginning in New York and moving on to London from September 15.
It follows years of debate around the use of ultra-thin models in the fashion and beauty industries, specifically around concerns that it is not only unhealthy for the women involved but can lead to eating disorders and self-esteem issues for women generally.
In a joint statement, the two brands said: "Respecting the dignity of every man and woman is at the heart of both groups' values.
"Having always cared for the well-being of models, LVMH and Kering feel that they have a specific responsibility, as leaders in the industry, to go one step further with their brands.
"This charter, which is applicable worldwide, reflects high standards of integrity, responsibility and respect for those concerned."
Francois-Henri Pinault, chairman and chief executive of Kering, said: "We hope to inspire the entire industry to follow suit, thus making a real difference in the working conditions of fashion models industry-wide."
Antoine Arnault, member of the LVMH board of directors, said: "The well-being of models is of great importance to us.
"As the leader in the luxury sector, we believe it is our role to be at the forefront of this initiative.
"We have the responsibility of building new standards for fashion and we hope to be followed by other players in our sector."