The Labour Day long weekend was anything but restful for Bruce Rodgers.

His phone started buzzing on the Friday night and didn't stop, with dozens of emails and calls all asking the same thing: Why had air cargo imports to Canada suddenly ground to a halt?

As executive director of the Canadian International Freight Forwarders Association (CIFFA) — the industry body for the national network of cargo handlers — Rodgers is used to dealing with the fallout from labour disruptions, accidents or even natural disasters. But not mysteries.

"We knew absolutely nothing. We were not aware of what transpired," he said. "Freight just wasn't moving."

Rodgers and his colleagues soon came to realize that Transport Canada had imposed radical new rules for air cargo imports from 55 mostly European countries, with no prior warning. And as a consequence, next to nothing was being accepted onto in-bound flights.

The new rules demanded proof of an "established" business relationship between shippers and recipients, with at least six shipments over the previous 90 days, as well as documented payment histories for past transactions. It's a high bar many importers couldn't reach — and one that is still causing chaos.

But the oddest thing to Rodgers was that no one would explain why.

"We attempted to get information directly from Transport Canada. They claimed that due to the Aeronautics Act, they weren't able to disclose this information with the freight forwarders, who are responsible for controlling the movement of goods. They only shared it with the airlines," he said.

Canadian cargo handlers finally figured out what was happening through conversations with their U.S. counterparts, who were grappling with the same new demands: Someone was trying to smuggle incendiary devices onto passenger and cargo jets, raising the possibility of a devastating mid-air fire.

Ottawa 'deeply concerned' with Russia's activities

It is only in the last two weeks that the extent of the threat has become clear. On Oct. 25, authorities in Poland arrested four people over an alleged plan to send firebombs hidden within personal massagers to addresses in Europe and beyond. The shipments are now linked to two summer fires inside cargo warehouses in Germany and the U.K. — test runs, it seems, for the targeting of trans-Atlantic flights.

"The group's goal was also to test the transfer channel for such parcels, which were ultimately to be sent to the United States of America and Canada," Poland's National Prosecutor's Office said, with the entire plot allegedly orchestrated by Russian intelligence.

Canadian authorities are still reluctant to discuss the matter. Requests by CBC News for interviews with officials from the Canadian Security Intelligence Service, Public Safety Canada and Transport Canada were all declined this week.

But a spokesperson for Public Safety Canada did provide a brief statement, acknowledging that the federal government is "aware of and deeply concerned with Russia's intensifying campaign, from cyber incidents and disinformation operations to sabotage activities." The statement also notes that Ottawa raised its concerns directly to Russian officials and "unequivocally stated that any threat to the safety and security of Canadians is unacceptable."

A request for an interview with Air Canada was also declined, with the airline noting that it has a general policy of not discussing security matters.

Russia has denied having any hand in the planting of the firebombs, with President Vladimir Putin calling the allegations "utter rubbish."

But concerns over Russian intelligence activities across western Europe have been simmering for almost a year — with dozens of incidents, from train derailments and arsons, to planned attacks on U.S. military bases and even a plot to assassinate the CEO of a German arms manufacturer, all linked to Russian agents.

Last month, Bruno Kahl, the head of Germany's foreign intelligence service, or BND, warned that Russia's dirty tricks campaign was now at a "level previously unseen," while Ken McCallum, director general of Britain's MI5, accused Russia of being on a "sustained mission to generate mayhem on British and European streets."

WATCH | 4 arrested in Poland over alleged plot to mail explosives:

Poland arrests 4 in plot to mail explosives to Canada and U.S.

Authorities in Poland have arrested four people in connection with an alleged plot to mail explosives to Canada and the United States.

Alleged plot represents new level of threat

Keir Giles, a Russia expert with Chatham House, an independent policy institute in London, said the true extent of the sabotage has been difficult to track because until recently, many countries have been reticent to disclose details of attempts or damage suffered.

What is clear, however, is that many of the acts are being carried out by proxies — often criminal gang members — allegedly recruited and paid by Russian intelligence.

"After the full-scale invasion of Ukraine, Europe got a bit of a holiday from these campaigns because the Russian intelligence services that were previously roaming the continent carrying out these attacks were fully occupied in Ukraine itself," Giles said. "What has changed now is that Russia has found a means of spreading its attacks further, with people who it can recruit to carry out attacks on behalf of Russia, not even necessarily knowing what they're attacking or why."

Giles, the author of a forthcoming book, Who Will Defend Europe?: An Awakened Russia and a Sleeping Continent, said the uptick in surveillance of, and attacks against, railways, airports and critical infrastructure over the past months is a worrying trend.

"One of the worst-case scenarios is that this could be Russia actually ... preparing the ground for a full-scale attack on a NATO member," Giles said. "Certainly a lot of the activities we're seeing going on match what we were expecting to see in those circumstances."

But the alleged plot against passenger and cargo planes represents a whole new level of threat, as evidenced by the swift and far-reaching rule changes for cargo.

"We haven't seen Russia planning for mass casualty events against Western capitals, whether by sponsoring terrorist groups to carry them out or through some other means of intervention," Giles said. "And now I think we have found it. This is Russia practising for killing large numbers of people in a terrorist attack."

Whether the incendiary devices were actually intended to bring down a plane or simply induce fear remains unknown — at least to the general public.

But their impact on trade, in Canada and abroad, continues to be felt. The tough, new air-shipping rules will remain in place for the foreseeable future, the CIFFA's Rodgers said, and so does the bottleneck for imports.

He still chafes at Transport Canada's close-lipped approach to the problem.

"It's frustrating," Rodgers said. "We need the information to help the government put in better controls, safer controls for the health, safety and security of Canadians. That's the role that we play.

"There's better, better measures that could have been implemented," he said. "My belief is that they truly don't understand the way trade moves."

Jonathon Gatehouse can be contacted via email at jonathon.gatehouse@cbc.ca, or reached via the CBC's digitally encrypted Securedrop system at https://www.cbc.ca/securedrop/