Britain introduced a two-week quarantine on Monday for most people arriving from abroad to try to limit the spread of the coronavirus. The decision has, however, sparked condemnation from the ailing aviation sector, which claims it could cost tens of thousands of jobs.

British residents and overseas visitors will have to comply with the 14-day self-isolation rules or face a £1,000 ($1,250, 1,125-euro) fine or prosecution.

Critics question why Britain, which has been hardest hit by COVID-19 in Europe and is only gradually easing a lockdown, is inflicting more pain on hotels and airlines by reducing travel from countries with fewer virus cases.

British Airways and budget carriers EasyJet and Ryanair have launched joint legal proceedings against the government over what they called a “disproportionate and unfair” step.

Ryanair boss Michael O’Leary told Sky News television on Monday the plan was “useless” and unenforceable, and said it would “devastate thousands of jobs in British tourism”.

The chief executive of London’s Heathrow, John Holland-Kaye, told the City AM newspaper it could lead to the loss of potentially 25,000 jobs at his airport — a third of staff.

But Health Secretary Matt Hancock said the new rules made sense because “the proportion of infections that come from abroad increases” as Britain’s own caseload drops.

“We’ve got to take an approach that starts with caution,” he told Sky News.

To enter Britain by plane, train, road or sea, travellers must provide details of their journey and the address where they will self-isolate.

How the quarantine will be implemented differs between Britain’s devolved nations, and the measures will be assessed every three weeks.

Exemptions are being made in several cases — including for lorry drivers, “essential” healthcare workers and people travelling from Ireland who have been there for at least two weeks.