The British Soft Drinks Association developed the code in conjunction with retailer representatives. It is set to be published at the end of the month.
Coca-Cola Enterprises, Britvic and GSK have all agreed to sign it, but Red Bull, which is not a member of the BSDA, has so far declined to take part or comment, despite being approached.
The code of practice is designed to give consumers and retailers an official industry stance on the healthiness of stimulant drinks and is a response to negative publicity about the drinks and their effect on children in particular.
"Energy drinks are safe and play an important role for many people, but the soft drinks industry believes soft drinks high in caffeine are not suitable for children because of their stimulant effects," said Richard Laming, public affairs manager at the BSDA.
"This code will support those parents, schools and retailers that wish to restrict the consumption of high-caffeine content soft drinks by children."
Under the code, packaging on drinks containing more than 150mg of caffeine per litre, as well as company websites where the products are featured, must carry the warning 'Not suitable for children, pregnant women and persons sensitive to caffeine'.
In addition, such drinks would not be advertised, marketed or promoted to children under 16.
CCE, which owns Relentless and Monster, already features on-pack warnings that pregnant women, children and people with sensitivity to caffeine should not consume the drinks.
But the new code will not apply to energy shots, as many manufacturers classify shots as food supplements and not drinks. It therefore wasn't clear whether manufacturers believe they should not be retailed to under 16s, said Association of Convenience Stores public affairs director Shane Brennan. If this was the case, "it had not been made clear to the trade", he added.
This week CCE launched 90ml concentrated Monster energy shots, pointing out it was an adult product.
"They are not a thirst-quenching drink hence the small pack size. They contain a similar amount of caffeine as a medium-serve latte or cappuccino from a coffee shop," said a CCE spokeswoman. "Our advice to retailers is to position shots on counter and away from products aimed at younger consumers."