Questions are being raised about how boxer Mike Tyson, a felon with multiple convictions, gained entry to Canada last week.

The former heavyweight champion was in Toronto for his sparsely attended one-man show at the Air Canada Centre.

Questions about the entry of a felon were initially drowned out by Tyson's antics during the visit.

He got into an on-air verbal dust-up with a CP24 news anchor who asked him about his 1992 rape conviction. He also made a high-profile visit to troubled Toronto Mayor Rob Ford, calling him "the best mayor in Toronto's history."

An array of celebrities with past criminal convictions have been turned away at the border over the years. Household diva Martha Stewart was denied entry in 2005 because of a conviction for a white-collar crime. American actor Wes Bentley tried to promote a movie at the Toronto film festival in 2012, but was turned back because of a prior drug arrest.

The Canada Border Services Agency cited privacy laws in refusing to provide details about Tyson's entry. His U.S. publicist didn't reply to queries.

Randall Garrison, the NDP public safety critic, said he's puzzled by the Tyson case. He also pointed out that Conrad Black was allowed into Canada in 2012, despite his convictions in the United States and the fact he had abandoned his Canadian citizenship.

"This is a government that claims to have a tough-on-crime agenda but then we see these absurd exemptions at the border when they appear to forget all about that," he said.

"If the government's not responsible, it should be asking questions about why Mike Tyson was allowed in."

'It's really weird'

Michael Niren, a Toronto immigration lawyer, says he hears every day from people turned away at the border owing to past criminal records not as serious as Tyson's.

"It's really weird," he said.

"Maybe it's his notoriety. We're all human, and I know there's a big star-struck factor. We have clients who aren't known, with lesser offences, who have a harder time getting through than those who have more notoriety. But, you know, Mike Tyson apparently has the cool factor."

Under border guidelines, convicted felons can apply for a rehabilitation certificate through a Canadian embassy or consulate and present it at the border if their crimes are more than five years in the past.

They can also be "deemed rehabilitated" at the border by an immigration officer, says the border agency.

While Tyson's rape conviction was in 1992, there have been more recent offences, including assault charges in 1998 and drunk driving and drug possession convictions in 2007.

In many cases, Niren says, convicted felons simply divulge their criminal past at the border and the immigration officer uses his or her discretion to determine whether there's any risk in allowing entry. If they deem the felon "rehabilitated," they issue a so-called temporary resident permit.

"The immigration officers are supposed to follow guidelines, of course, but at the end of the day it is discretionary and they do make judgment calls," Niren said.

He added he thinks the government's regulations on convicted felons are too onerous.

"Should people be doubly punished in terms of their mobility rights?" he asked.