The UK’s bizarre decision to implement a quarantine on most people entering the country is being challenged by an unlikely trio of airlines.

UK flagship British Airways (BA), UK LCC easyJet and Irish LCC Ryanair are usually strong competitors that are not necessarily “nice” in their rivalry. Just last year, Ryanair took one of its top executives to court because he left to take up a position at easyJet.

But the UK government’s new quarantine rule has incensed and united these carriers.

Beginning June 8, the majority of people entering the UK are required to provide their journey and contact details to the government, then self-isolate at their designated address for 14 days.

The UK experienced one of Europe’s worst cases of COVID-19 infections and deaths. As it slowly pulls out of the pandemic and loosens lockdown restrictions, concern about a second wave coming from outside is understandable. But if that is truly the government’s motivation, it hardly needs a quarantine rule. Most countries outside of the UK, including many European nations, have had far lower infection and death rates. For residents of those countries, the UK was probably already very low on their “need to visit” list this summer or even this year.

Maybe the UK government is focused not so much on dissuading foreigners—despite their potential to bring tourism and trade dollars to a financially wrecked country—but on keeping its own citizens at home? Why might that be? Potentially because many Brits like to spend their vacations in the warmer, sunnier climes of their European neighbors.

This year, of course, the UK left the European Union (EU) after a successful campaign led by now-Prime Minister Boris Johnson and his closest allies who make up his cabinet. As they made Brexit a reality in January, they were determined to showcase a new Britain, financially successful independent of the EU. The pandemic has already blasted a hole through that, with the remaining EU countries knitting together a massive €750 billion ($836 billion) stimulus package that will outweigh and out-compete anything the UK can do.

With summer arriving and Brits itching to get out, what better way to keep their vacation pounds and pennies inside the border than to threaten another 14-day lockdown on anyone who leaves? If the quarantine rule was purely science based, it would not have any exemptions. But it has several, including for road haulage and freight workers, medical and care professionals, people arriving for pre-arranged medical treatment, passengers in transit, seasonal agricultural workers and UK residents who ordinarily travel overseas at least once a week for work.

The last two categories are particularly suspicious. The UK already faced a shortage of harvest pickers this summer because many of these workers were EU citizens, for whom Brexit made travel and work in the UK more difficult. And why would UK residents flitting back and forth to other countries on a weekly basis pose less of a virus risk than those who travel once or twice a year?

With no specific explanation forthcoming from the UK government for its quarantine rationale—and with no timeline for when the restrictions might be lifted—the rule looks politically motivated. Worse, it will inspire political tit-for-tats. France has already reciprocated with similar restrictions on British travelers.

Ultimately, some UK citizens may still believe it’s worth spending two weeks at home after a week’s vacation in Tenerife or Tuscany. But no foreigner will voluntarily enter another country’s quarantine, so they will take their vacation and trade dollars elsewhere. Vacation choices might revert to the UK in 2021; business deals, when done, tend to be permanent.

Meanwhile, the UK’s airlines—a huge driver of the nation’s GDP—will be severely damaged by this rule. British Airways, in particular, cannot restart its predominantly international network until the quarantine is lifted. Yet its European rivals, including Air France, Alitalia, Lufthansa and KLM, are getting head starts in government financial aid and destination reopenings.

As the CEO of BA’s parent company International Airlines Group, Willie Walsh, said, the quarantine is a “torpedo” in BA’s restart plans.

In a joint statement issued as the quarantine rule went into effect, BA, easyJet and Ryanair said it would have a “devastating effect on UK’s tourism industry and will destroy (even more) thousands of jobs in this unprecedented crisis.”

They are right. The UK government’s quarantine rule smells political. Allowed to stay in place even a few weeks, it will kill more than it cures.