The travel industry has condemned the government's quarantine rules, warning the mandatory two-week isolation will deter visitors and put jobs at risk.
From 8 June all passengers arriving in the UK must self-isolate for 14 days.
The manufacturing industry has added to the criticism, warning fewer flights will restrict imports and exports.
The boss of the UK's biggest airport services company, Swissport, said the plan could deliver a "killer blow" to the tourism sector.
Michael O'Leary, chief executive of Ryanair, echoed those concerns, saying the requirement to self-isolate would "significantly reduce European visitors".
Speaking on BBC Breakfast, Mr O'Leary said most countries in Europe have a lower rate of coronavirus than the UK.
At a time when "Italy, Greece, Spain and Portugal are removing visitor restrictions, the UK is imposing them," he said.
Swissport chief Jason Holt questioned why the rules were being put in place now.
Speaking to the BBC's Today programme, he said: "If it's so important and it's so relevant to the virus, and we all want the country to be safe, why wasn't this done in March? That's why everybody's quite confused on this."
More than 200 travel companies have written to the government asking for the new rules to be scrapped, while some MPs have also raised concerns.
The boss of tour operator Red Savannah said the government had failed to listen to the concerns of the travel industry.
"We are none the wiser as to the science behind the rationale for quarantine," said George Morgan-Grenville.
"It is the wrong policy that is going to cause untold misery for hundreds of thousands of people who will now very likely be made redundant."
But the government says the quarantine period is a "proportionate and time-limited approach'' to protect public health.
On Wednesday, Home Secretary Priti Patel told Parliament imported coronavirus cases now ''pose a more significant threat''.
"We are past the peak but we are now more vulnerable to infections being brought in from abroad," she said.
The manufacturing industry has warned the quarantine rules will have knock on effects for freight, and that will hamper the recovery of some businesses.
Speaking to a committee of senior MPs, Stephen Phipson, the head of the manufacturers' association Make UK, said "passenger aircraft are really important for freight. The belly of the aircraft carries freight. Heathrow is the largest port in the country."
"For import and export in manufacturing that passenger freight traffic is vital", he said.
He described the quarantine rules as "disappointing from that point of view".
From Sunday, all passengers arriving in the UK by plane, ferry or train will have to provide an address where they will remain for 14 days.
Surprise visits will be used to check they are following the quarantine rules. Those in England could be fined up to £1,000 if they are not at home.
A spokesman for the trade body Airlines UK said the government needed to clarify whether people from some countries with low infection rates would be exempt from quarantine rules, under a so-called air bridge.
"If the government leave it too late we run the risk of the summer season being over and losing out to other countries who are starting to open up their borders now," he said.
Swissport, which handles airport ground services and cargo, earned more than €3bn (£2.8bn) in revenue in 2019 but the coronavirus crisis has reduced revenue by 95%, according to Mr Holt.
The company has furloughed most of its 6,000 UK staff.
Mr Holt said they would remain on the Job Retention Scheme until the government's future travel policies became clear.
He said Swissport had lobbied the government to avoid introducing quarantine, but the company was now hoping the rules will only be in place for short time.
"We're really hoping no more than three weeks," he said. If it goes beyond that it could do "irredeemable damage to the sector".