Billboards advertising junk food offered by vendors like McDonald’s might be banned from London’s Underground rail and bus network under new plans announced by the city’s mayor as part of his efforts to tackle rising levels of childhood obesity.

Sadiq Khan, elected mayor of London in 2016, said in a statement he wanted to reduce the influence and pressure put on children and families to make unhealthy choices. Nearly 40 percent of 10- and 11-year-olds in the capital are overweight or obese, one of the highest rates in Europe, the mayor’s office said.

A large percentage of the advertising that would be affected comes from “a handful” of major companies and brands, a spokesman Transport for London said by email. A spokeswoman for McDonald’s, whose advertisements are a regular fixture at London Underground stations, said the company shares the mayor’s ambition to reduce childhood obesity.

“We take our responsibilities extremely seriously and have always complied with and exceeded the stringent marketing requirements placed on us – some of the strictest in the world,” she said.

Stephen Woodford, chief executive of the Advertising Association, a lobby group for the U.K. ad industry, said research has shown an advertising ban would have little impact on the wider societal issues that drive obesity, which is caused by the interaction of many factors.

Amsterdam is among other cities to have introduced similar measures, bringing in a ban on advertisements for unhealthy food on its transport network at the start of this year.