Airlines cannot add on fuel surcharge fees for flights that have already been paid for - as long as the flight was bought in the EU, it has been announced.
The European Commission (EC) has said that carriers must show their flight prices and cannot adjust them after they have been purchased.
The EC website explained: 'Airlines are required to display final ticket prices upfront thanks to the Air Services Regulation, which ensure transparent pricing of airfares.
'This means they are not allowed to charge extra fees retroactively due to fuel surcharges.'
It added that travellers affected by cancellations continue to benefit from air passenger rights.
They are entitled to reimbursement, re-routing or return, assistance at the airport and compensation for last-minute cancellations.
Airlines may only be exempt from financial compensation when they can prove that the cancellation was caused by extraordinary circumstances.
'High fuel prices should not be considered an extraordinary circumstance,' the EC went on to say.
Volotea has already begun to introduce add-on fees amid the jet fuel crisis - but the European Commission has now banned the airline from doing so
The new rule comes amid fears of crippling fuel shortages linked to the war in Iran and disruption in the Strait of Hormuz, a vital route for oil tankers.
Jet fuel prices doubled from roughly $100 (£73) per barrel in late February to around $200 (£146) per barrel in early April following disruption caused by the conflict in the Middle East.
The EC has outlined other measures in place to combat the ongoing jet fuel crisis.
To help avoid the closure of certain routes, airlines can be exempted from the 90 per cent fuel uplift rule under the ReFuelEU Aviation - where airlines leaving EU airports must refuel most of their annual requirement at a specific EU hub.
Regarding airport slots, airlines may be exempt from the usual landing and take-off slot obligations due to fuel supply issues at airports.
It comes after Spanish budget airline Volotea charged customers an extra fee of up to €14 (£12) once passengers had bought tickets, due to fuel surcharges.
Some airlines in the UK have already announced they will not impose surcharges on flights.
Jet2 confirmed it will not introduce surcharges on any booked flights or holidays to cover cost increases, for example jet fuel, assuring customers that the price they book is the price they will pay.
It comes as a great relief to travellers, as there has been continued speculation that some airlines may have to introduce such fees to help tackle the rising costs.
Another travel company freezing prices is One Traveller, a solo escorted tour operator for the over-50s.
Jet2 announced it won't introduce surcharges on any booked flights or holidays
The company has announced that bookings made before 18 May will offer price guarantee regardless of any increase in fuel surcharges that may come into play in the coming weeks.
Additionally, the tour operator's Deposit Guarantee Scheme that has been in place on selected tours is now available on ALL One Traveller holidays booked before 18 May 2026.
Meanwhile, On The Beach and BA Holidays guaranteed Which? earlier this month that they 'definitely' would not add surcharges to their customers.
Other travel companies including Trailfinders, Destination2, Kuoni, Jet2holidays, Olympic Holidays and Beachcomber Tours all promised they would not introduce unexpected surcharges too.
Meanwhile, LoveHolidays told the Which? it 'has not imposed surcharges before and we have no intention of doing so in the future'.
As for LastMinute.com, the booking site said it would not surcharge but couldn't promise customers would not face additional costs from airlines.
On the flip side, some airlines have warned they are having to reconsider their pricing if the situation continues, including IAG which owns British Airways.
The carrier told the Daily Mail previously: 'We are not seeing jet fuel supply interruptions, but fuel prices have risen sharply and, despite our hedging strategy which gives some shorter term mitigation, we are not immune to the impact.
'Like other carriers, IAG airlines are making some pricing adjustments to reflect these higher fuel costs.'
The spokesperson added: 'Our airlines will continue to monitor and respond to the situation and as long as these pressures continue, flexibility from government, including on slot alleviation, would ensure airlines can continue to operate as efficiently as possible and manage sustained cost challenges while keeping people and trade moving.'