Britain's travel and airline industries have lambasted new proposals published by the government's Global Travel Taskforce on Friday.
The announcement includes a traffic light system, which categorises countries based on risk as well as COVID tests, even for people arriving from low-risk green destinations.
The need for those who are vaccinated to still be expected to pay for gold standard PCR tests on their return to Britain has been called a "hammer blow" for the travel industry.
EasyJet (EZJ.L) chief executive Johan Lundgren said the plan was "a blow to all travellers" and risked "making flying only for the wealthy."
"As the rest of British society and the economy opens up, it makes no sense to treat travel, particularly to low-risk countries, differently," he added.
Despite the announcement, the Global Travel Taskforce (GTTF) did not confirm whether foreign holidays will be permitted from 17 May, but it did suggest that it could still resume "in an accessible and affordable way."
The move has put more pressure on the sector which has already been struggling due to the pandemic.
Low budget airline Jet2 (JET2.L) and Jet2holidays announced on Friday that because of the government’s lack of clarity on Britain's return to travel, it has extended its flight and holiday suspension to 23 June.
"Because of the continued uncertainty that the framework provides, it is with a heavy heart that we have taken the decision to extend the suspension of flights and holidays up to and including 23rd June 2021, " the company said.
Jet2 said that it will "cancel the bookings and offer full refunds" to customers who are affected by any of the changes.
Steve Heapy, CEO of Jet2, called for further clarity on a “cost-effective” COVID-19 testing regime for travellers.
Shares in the company plummeted nearly 5% in morning trade in London.
May was the earliest month when international travel was expected to resume under prime minister Boris Johnson's roadmap out of lockdown.
Transport secretary Grant Shapps has said that the UK will work with the travel sector and private COVID testing providers to reduce the cost of foreign trips.
But Shapps voiced "concerns" over the costs of the tests, adding that the government was committed to driving down the price of these by working with the private sector.
WATCH: People can now think about booking foreign holidays, says transport secretary
This could lead to free COVID-19 tests before departure, and less expensive tests when holidaymakers return.
Aito chairman, Chris Rowles said the plans "smack of elitism."
He added: "While green destination holidaymakers will not need to quarantine on arrival back in the UK unless their test results prove positive, it is certainly not an encouraging start point.
"If those travelling have been vaccinated, whether one jab or two, that should suffice – otherwise, what on earth is the point of the UK’s highly successful vaccination project and the proposed travel certification mentioned?"
Meanwhile, Abta chief executive Mark Tanzer said that the requirement for a PCR test when arriving back from a "green list" country may prove a "cost-barrier" for many travellers, he welcomed the fact that the government has committed to engaging with industry on the issue.
British Travel Association (BTA) chief executive Clive Wratten described the GTTF report as "yet another hammer blow" to the business travel industry.
The British Chamber of Commerce (BCC) "welcomed" the announcement, but warned that unanswered questions remained. It called on the government to "redouble their efforts" to provide further clarity on the green list "as quickly as possible" and ensure "PCR test are affordable and accessible to all”
However, there have been warnings that reliance on lateral flow testing could lead to a third wave COVID infections.
Ben Paglia, managing director of Akea Life, said: "The government’s suggestion to allow airline passengers to also potentially administer their own lateral flow tests would also set a very dangerous precedent and hinder the accuracy of results."
He added that the "number of false negatives can increase significantly simply due to the lack of understanding people will have in testing themselves."
While it is not yet clear which countries will be green, amber or red, the government said it would announce it by early May.
The traffic light system will rank countries green, amber or red according to risk level, which are based on vaccination progress, COVID-19 cases and variants.
Under the plans, those returning from "green" listed countries will not need to quarantine on return, but have to take a pre-departure test — the government has not specified which type — as well as a PCR test on return to the UK.
Travellers coming into the UK from "amber" countries will need to quarantine for 10 days, as well as take a pre-departure test and two PCR tests.
The government will keep a close eye on countries that could go from green to amber, to implement proper measures if needed.
Those returning from "red" destinations will have to pay for a 10-day stay in a managed quarantine hotel, as well as a pre-departure test and two PCR tests.
The aviation industry has been hit hard by the pandemic amid grounded flights and global lockdowns.
Many airlines were forced to make difficult decisions in order to save their businesses including cutting jobs to save cash, while trying to navigate the ever-changing landscape of government measures.
The International Air Transport Association (IATA) said the industry reported an estimated net loss of $118.5bn (£85.7bn) in 2020, a deeper rescission of its $84.3bn forecast in June last year.
A net loss of $38.7bn is also expected in 2021, more than double the projected $15.8bn loss six months ago.
WATCH: Should I book a holiday in 2021?