Owen Carey, 18, suffered a fatal allergic reaction in April 2017 after eating half a chicken burger coated in buttermilk from the chain's O2 Arena restaurant.
The BBC reports that a coroner ruled he was not told about the allergen that led to his death and the menu did not indicate the burger contained dairy.
Speaking outside Southwark Coroner's Court Carey's sister Emma Kocher called for the introduction of 'Owen's Law' to improve labelling of dishes.
"The food industry should put the safety of their customers first and be proactive about protecting those with allergies," she said.
"It is simply not good enough to have a policy which relies on verbal communication between the customer and their server which often takes place in a busy, noisy restaurant where the turnover of staff is high and many of their customers are very young."
During the case assistant coroner Briony Ballard suggested restaurants mark allergens on menus with a "big A" to "prevent future deaths".
Aimee Leitner-Hopps, Byron’s head of food and compliance, denied any wrongdoing by the restaurant group and said customers should inform staff of their allergies.
But she added that Byron’s menu was changed in November 2017 to highlight that the chicken burger was ‘marinaded in buttermilk’, and employees now ask customers outright about their allergies.
After the hearing Byron CEO Simon Wilkinson told the BBC: "We take allergies extremely seriously and have robust procedures in place and although those procedures were in line with all the rules and guidelines, we train our staff to respond in the right way.
"It's clear current rules and requirements are not enough and the industry needs to do more - more to help customers with allergies and more to raise awareness of the risks of allergies."
The hospitality industry has faced greater scrutiny over allergen labelling following the death of teenager Natasha Ednan-Laperouse, who suffered a fatal reaction to a Pret a Manger baguette in 2016.
The incident has led to the introduction of 'Natasha's Law', which from October 2021 will require foods such as packaged sandwiches and salads prepared in cafes to display a full list of ingredients.