With a deadly punch packed in a dose the size of a grain of sand, fentanyl is both lethal for its users and irresistible for traffickers looking to use Canada's postal service as a drug mule.

As the death toll from the illicit opioid rises in Canada, police chiefs across the country are renewing calls for an unprecedented change to the law that forbids police agencies from searching mail in transit with Canada Post.

The push to allow law enforcement to search mail and intercept illegal drugs before they arrive at their destination isn't new, but fentanyl's pervasiveness has made it more critical than ever, said the Canadian Association of Chiefs of Police, a national non-profit group based in Kanata, Ont.

Fentanyl is so potent, shipping it by mail in small quantities can still be lucrative for organized crime. (Cuyahoga County Medical Examiner's Office/The Associated Press)

"In light of the current crisis we're facing with fentanyl, there is a renewed sense of urgency for this to be addressed," said Mike Serr, co-chairman of the association's drug abuse committee and deputy police chief in Abbotsford, B.C.

The Canada Post Corporation Act prevents anyone from interfering with mail deliveries, including the police.

Police face roadblocks

Police are only allowed to search mail when it arrives at its destination, meaning law enforcement's hands are often tied, said Serr, whose association represents more than of 90 per cent of the police community in Canada.

"If we had the intelligence, we could not advise a Canada Post employee to search it on our behalf." - Deputy police Chief Mike Serr

He said recent court rulings have determined that postal workers cannot act as agents of the state when police ask them to intercept contraband during the postal delivery process.

"If we had the intelligence, we could not advise a Canada Post employee to search it on our behalf ... we would have to wait until it makes it to its final destination."

Fentanyl that's sold on the streets is cut in places like this drug lab in Burnaby, B.C. (Delta Police)

However, the Canada Border Services Agency and Canada Post staff can search mail on their own if a package appears to be suspicious.

100 times more powerful than heroin

Fentanyl is a synthethic opioid that's 100 times more powerful than heroin. Small amounts of fentanyl can be diluted — a process known as "cutting" — with other substances to reduce its potency while making more of the product, said Serr.

If the Canada Post Corporation Act is changed, police would still need judicial authorization such as a search warrant to go through mail in the process of being delivered by Canada Post. Police would have to convince a judge that a crime has taken place and a particular piece of mail is evidence of that crime to gain access.

It's the same process police currently use to search mail once it's arrived at its destination.

Guns, grenades being put through mail

The Canadian Association of Chiefs of Police adopted a resolution at its annual general meeting last year saying it would lobby for changes to the act.

The resolution states that in 2013, the RCMP along with the Canada Border Services Agency and the international police organization Interpol took part in a weeklong operation to disrupt the online sale of counterfeit and unlicensed medicine. They found illicit and fake medicines in 3,223 packages worth $1,032,514. Drugs like cocaine have also been shipped using the postal service, said Serr.

The resolution also states the association received a censored report from the RCMP that showed that guns, grenades, a rocket launcher, stun gun and dangerous chemicals were all shipped through the postal system.

No move from the government

The association has talked with Canada Post, the federal Justice Department, Public Safety Canada and legislators about the proposed changes to the act. So far, there hasn't been any concrete action, said Serr.

Mike Serr, co-chairman of the drug abuse committee with the Canadian Association of Chiefs of Police, says the laws surrounding Canada Post "ties law enforcement's hands." (CBC)

"We will continue to really push forward for this," he said. "We're reaching out to different ministers through the Canadian Association of Chiefs of Police to advocate ... for the change."

It would be premature to speculate on whether specific legislative reform is required at this point. - Federal Justice Department

The Justice Department said in an email that it is aware of the concerns expressed by law enforcement.

"Federal officials, alongside their provincial and territorial partners, are presently examining ways to strengthen the integrity of the postal system and prevent the shipment of contraband through it," it said.

"It would be premature to speculate on whether specific legislative reform is required at this point."

Privacy lawyer supports proposed changes

Canada Post also weighed in by email, saying it works with numerous agencies and police administrations to protect Canadians. It added that a team of postal inspectors monitors mail and protocols are in place to co-operate with police if an item is deemed suspicious.

David Fraser, a privacy lawyer with McInnes Cooper in Halifax, supports changes to the Canada Post Corporation Act. (McInnes Cooper)

Public Safety Canada did not respond to interview requests by deadline.

David Fraser, a leading privacy lawyer in Halifax, said he generally opposes the expansion of police powers.

Not this time.

"The Canada Post Act that says that the mail is sacred and it can't be detained, which is quaint," said Fraser, a partner with McInnes Cooper.

"But I think in the circumstances when you're dealing with very dangerous items that are going through the mail, it does make sense to intercept them at that point before they represent a risk to the public."