OTTAWA -- The federal government is coming under fire from the opposition Conservatives for failing to disclose how much a cannabis tracking system will cost -- just one of a host of proposed changes to be ushered in along with the legalization of marijuana.

Health Canada said the system would be designed to collect information about pot products from licensed producers, distributors and retailers, adding it would not track individual cannabis users.

The department also said it would allow businesses and regulators to trace all products and address recalls.

"They want to put a pot registry in, but they are not telling us about how much it is going to cost," said Conservative health critic Colin Carrie. "It is just basically more shady behaviour when it comes to this file."

The tracking would help to ensure cannabis is not being diverted to illegal markets, Health Canada said in a statement, given the government's stated and oft-repeated goal of limiting organized crime's footprint in the pot trade.

"Mandatory product track-and-trace systems are common features in other jurisdictions that have legalized cannabis for non-medical purposes," the department said.

The specific requirements of the system still need to be developed, Health Canada added, noting similar systems are used in the U.S. to gather information about cannabis products.

The department did not say how much the proposed tracking system would cost -- only that it intends to offset such costs through licensing and other fees.

The government's marijuana legislation tabled last week also failed to offer specifics on tax measures for the legalized regime.

Alistair MacGregor, the NDP's justice critic, said he is surprised the government can't offer more information.

"On the day this bill was announced, they did bring out the minister of national revenue," MacGregor said. "One of the biggest questions we have is the cost of implementing not just this registry but all of the enforcement measures; How much of this is going to be downloaded on to the provinces?"

On Thursday, thousands across the country are marking are annual pot celebrations known as 4-20 though some marijuana activists are expressing concern about the government's legalization efforts.

Alex Newcombe, a 31-year-old medicinal marijuana user attending 4-20 celebrations on Parliament Hill, said Thursday he is disappointed by the Liberal legislation introduced last week.

"It is not anything other than prohibition 2.0," Newcombe said, who is especially upset that the federal Liberals have not taken steps to decriminalize the drug in the interim.

"(Prime Minister Justin Trudeau) could decriminalize it at a moment's notice," he said. "He's the one stopping it at the moment -- we're calling him out on it."

The federal government has said repeatedly it has no plans to decriminalize marijuana until legalization is in place -- a goal it hopes to achieve by July 2018.

Trudeau, who admitted to smoking pot after becoming an MP, told Bloomberg on Thursday that Canada's legalization strategy is built around a recognition that marijuana is "not good" for the developing brains of young people.

"We need to do a better job of making it more difficult, at least as difficult as it is to access alcohol as it can be," he said.

Criminal organizations and street gangs collect billions every year from illicit marijuana sales, he added, noting this money is then funnelled into other criminal activities.

"So you put those two things together and realize we have a system that isn't working," Trudeau said.