A powerful tool authorities across Canada use to crack down on organized crime is itself under fire in a B.C. courtroom this week.

Several U.N. Gang members are filing a constitutional challenge, wanting to put limits on how much information Canada's tax collectors can give police when investigating organized crime.

"There is no equivalent to the right to silence within the Canada Revenue Agency investigation," said the U.N. Gang's lawyer, Martin Peters, in Federal Court in Vancouver this week, adding that this contravenes sections 7 and 8 of the Canadian Charter of Rights and Freedoms.

But losing the ability to share information with the CRA would hobble police investigations into organized crime, said Sgt. David Gray of the RCMP's Integrated Proceeds of Crime unit.

"We'd be at a standstill in our investigation," said Gray to CTV News. "You'd see one less tool in our toolbelt and it would add to the strength of organized crime, alling them to proliferate in wealth and power."

The U.N. gang -- named by police as among the most violent gangs in the Lower Mainland -- has been under investigation by police since at least 2006.

Police have been trying a relatively new tactic to corner them -- using the rules in the Income Tax Act, demanding that they declare what could be illegal income, which would result in the seizure of assets.

If they don't declare what could be illegal income, they could be found guilty of tax evasion.

Sound familiar? It's the same strategy that nailed famous Chicago gangster Al Capone in the 1930s.

The plaintiffs are alleging that because they are forced to declare their income, they are giving up a right to silence.

Lawyers for the Minister of National Revenue are expected to tell the court that the agencies are just doing their job -- trying to keep the Lower Mainland safe and securing tax income with the available tools.

In early 2007, Combined Forces Special Enforcement Unit investigator Mike Ryan forwarded a list of 43 alleged U.N. gangsters to the Canada Revenue Agency, suggesting that it would be useful to look into their finances.

Wayne Fjoser of the Canada Revenue Agency received the letter and a year later decided to begin to audit some of the names on the list.

The case offers an interesting insight into the face-to-face meetings between auditors and alleged gangsters -- many of them happened in the middle of the night, and some outside a suburban movie theatre.

"They were shaking people out of bed in the middle of the night, restraining people from leaving," said Peters to the court. "It was heavy-handed and abusive."

The case is being heard this week.

With a report from CTV British Columbia's Jon Woodward