Actor Seth Rogen is joining calls for the Canadian government to expunge the criminal records of drug users who were convicted of simple pot possession.

Rogen used this year's 4/20 event to draw attention to the Cannabis Amnesty campaign, which wants the government to issue "blanket pardons" for the offence now that recreational marijuana has been legalized across the country.

"4/20 is also about activism and I'd like to raise awareness to some of the injustices that revolve around cannabis in Canada," Rogen wrote to his 6.7 million Instagram followers on Saturday.

The federal government has already introduced a bill making it easier for people to obtain a pardon for cannabis possession, but critics argue it doesn't go far enough.

Pardons, also known as record suspensions, make it easier for former convicts to find work, but their criminal records are only sealed, not erased.

"Canadians deserve freedom, not forgiveness," Rogen said.

According to the Cannabis Amnesty campaign, more than half a million Canadians currently have criminal records relating to simple marijuana possession, which make it difficult to "find meaningful work, volunteer and travel."

"No Canadian should be burdened with a criminal record for a minor, non-harmful act," the campaign's website reads. "Canada has an opportunity to become a world leader by implementing a cannabis policy driven by compassion and evidence, not stigma and fear."

One of the main arguments for full record expungements is the claim that marijuana laws have been a bigger burden on black and Indigenous Canadians than white people. Cannabis Amnesty pointed to reports that found black Toronto residents were more likely to be arrested for pot possession than white residents, despite similar rates of use.

"Decades of unfair and unequal enforcement of cannabis laws has meant that marginalized and racialized Canadians have been disproportionately burdened by cannabis convictions," its website says.

NDP Leader Jagmeet Singh has echoed those concerns, and publicly supported an immediate deletion of criminal records related to simple possession since before legalization took effect last year.

"For some people in Canada, and in some places, pot has been effectively legal for years," Singh said in October. "But depending on who you are, the colour of your skin, and where you live, there’s a different set of rules."

The Cannabis Amnesty campaign also includes a petition calling on the federal government to enact mass-pardoning legislation, which had already been signed more than 8,700 times by the morning of 4/20.