, which includes tour operator Mr & Mrs Smith as well as luxury hotels The Ritz and Hyatt Regency, said: "The very last thing the travel industry needs is a mandatory quarantine imposed on all arriving passengers which will deter foreign visitors from coming here."
It added that it will also "deter UK visitors from traveling abroad, and most likely cause other countries to impose reciprocal quarantine requirements on British visitors".
France has already warned that they would enforce similar measures in response to the UK guidelines.
A spokesperson for France's Interior Minister said: "We take note of the British government’s decision and we regret it.
"France is ready to put in place a reciprocal measure as soon as the system comes into force on the British side."
While the open letter praised the government for handling the pandemic, they also warned that the quarantine period wasn't enforced during the peak of the crisis, when international travel was still at high levels.
The letter continued: "Many people urged the government to impose quarantine regulations during the early phases of Covid-19.
"Instead, no action was taken and flights from infected countries were allowed to land, disgorging thousands of potentially affected passengers into the wider community."
A Home Office spokesperson told MarketWatch, who first saw the letter, that the quarantine is the right way to prevent a "devastating second wave".
UK airlines have already slammed the two-week isolation measures, with Ryanair boss Michael O'Leary calling it "idiotic and unimplementable."
British Airways warned that their return to the skies in July could be delayed by the quarantine too.
Another option being considered are "air bridges" which are an agreement between two countries to let nationals travel between them without needing to quarantine for 14 days.
Prime Minister Boris Johnson confirmed the Government is looking at air bridges with other countries earlier this week.
Portugal and Greece are two countries being considered to join up with the UK, amid hopes they could start as soon as next month.
Travel corridors between the UK and Spain could open between destinations such as Birmingham and Majorca first, if they have lower cases of coronavirus.