Doug Ford fired off yet another strongly-worded letter to Prime Minister Justin Trudeau on May 12, urging him to act on the premier's request to strengthen Canada's border measures.

In the letter, Ford wrote that he's disappointed that there's been "no action on any of these requests," which include reducing international flights, closing the land border loophole with three-day hotel quarantine at high-traffic crossings, and mandatory COVID-19 tests for domestic travellers entering Ontario.

"Further, we have seen alarming reports that one in three individuals travelling internationally by air have also been able to bypass this requirement," he wrote, citing data from the Public Health Agency of Canada that around 88,000 air travellers have been exempt from hotel quarantine.

The premier demands in his letter that Trudeau "provide Canadians with a clear explanation" of why these travellers were exempt, and details about where these travellers came from.

Last week, Trudeau responded to Ford's campaign to tighten border measures.

"It's been a week since we've received that request directly from the premier that they haven't followed up on except with personal attacks, which doesn't make sense and quite frankly won't help Ontarians," he said. "If the Ontario government wants to do more to restrict the volume of people coming into Ontario, we are more than happy to work with them on it."

Ontario officials are concerned about the hotel quarantine "loophole"

Ford isn't the only one who is concerned about a loophole that allows international travellers to skip hotel quarantine.

Ontario's Health Minister and Solicitor General wrote a letter to the federal government recently about the "deeply troubling" loophole, which allows travellers to cross the Canada-U.S. border on foot.

"There are reports of international travelers booking return flights into nearby United States airports, taking a taxi or limousine to a United States-Canada land border crossing, and subsequently walking or driving across the border," the officials wrote.

Along with Premier Ford, they've requested that a three-day mandatory quarantine be set up at hotels at busy crossings like Niagara, Windsor, Sarnia, and Brockville.