The Irish Heart Foundation has called on the Government to protect children from online junk food marketing.
Research commissioned by the organisation showed that three quarters of Irish teenagers said they see junk food advertised "often" in their daily lives, particularly through social media.
The study of 500 parents and 500 teenagers found that over a third of teenagers ate junk food after seeing unhealthy food ads.
Launching its "Stop Targeting Food" campaign, the foundation said this type of advertising is fueling the obesity crisis.
It said social media is where most teens are exposed to high fat, sugar and salt foods, particularly on TikTok, Snapchat, YouTube and Instagram - platforms teenagers access on average 38 times a day.
Irish Heart Foundation's Director of Advocacy Chris Macey called on the Government to take action.
"We want a complete ban on online junk food marketing, we want the broadcast watershed moved from six o'clock to nine o'clock and we want a ban on public transport and other state-owned buildings and public infrastructure. We want a ban on all junk food marketing on those."
The survey found that almost one third of teenagers would be in favour of banning junk food adverts to under 18s.
We need your consent to load this YouTube contentWe use YouTube to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage PreferencesDirector of Empathy Research Robbie Clarke said: "76% said they feel they're advertising to them often or very often and the degree to which social media is playing a role in that.
"But also it goes further than social media, it is TV advertising, out of home advertising, billboard advertising."
The Irish Heart Foundation said that one in 20 of this generation's children will die prematurely due to overweight and obesity.
The organisation says it is seeing children as young as six presenting to doctors with high blood pressure.
The study also found that 45% of parents are very worried about their child's consumption of junk food and half said it was becoming more difficult to get their teenager to eat healthily.
The Irish Heart Foundation has appealed to the public to sign an online petition calling for the introduction of the Public Health (Obesity) Act at Irishheart.ie.
Associate Professor of Marketing at Trinity College Dublin Norah Campbell said the industry wants to do more to protect children.
She said: "The scale and scope of marketing now is such that there is no putting the genie back in the bottle."
"What we need now is regulation in order to make the competitive landscape fairer for everyone - including the food industry."
Health campaigners say healthy habits develop in early life and that Government action on online junk food advertisements is urgently needed to curb the obesity epidemic.