A proposed law that would make it illegal for protesters to cover their faces during a riot or unlawful assembly isn't necessary because there's already a law against wearing a disguise to commit an offence, MPs heard today.

But the MP who wrote the bill says that current law isn't strong enough.

Bill C-309 is intended to make it easier for police to identify and charge violent rioters, Conservative MP Blake Richards says. But James Stribopoulos, an associate professor at York University's Osgoode Hall law school, told MPs on the House justice committee that the Criminal Code already makes it illegal for anyone to wear a disguise to commit an indictable offence.

It's also important to be careful the law doesn't infringe on the rights of those who are in the area with no intent to riot, and that police don't pre-emptively arrest lawful protesters who are wearing masks, Stribopoulos said.

The committee also heard from former RCMP officer Patrick Webb, who said the bill would give police an extra tool to prosecute people who trash property or get violent during riots. Webb worked for the RCMP for 31 years, including at several G8 summits and other public events that drew large crowds and protests.

It's difficult to charge and prosecute somebody, Webb told the committee, if you can't identify them and link them to the crime. Masks make it harder to successfully identify rioters.

Richards says police officers have told him the existing law is designed more to catch people who wear a mask to rob a bank than rioters who cover their faces.

"They've been very clear with me that it's a very difficult section for them to be able to apply to these types of events, unlawful assemblies and riots," he said. "So there actually is a need for a tool that is specifically amending the sections of the criminal code that deal with unlawful assemblies and riots so that it can be applied to this type of situation."

Participating in a riot is an indictable offence that would be covered under the existing provision. But taking part in an unlawful assembly is a less serious crime, which wouldn't be covered. An unlawful assembly is a gathering that causes fear.

It's up to city officials to decide what constitutes a riot, Richards said.

Opposition MPs ran out the clock

Opposition MPs talked for the full hour set aside Tuesday to go through the bill one clause at a time. That's the last step in a committee before returning legislation to the House of Commons for a vote.

Richards said he was disappointed because the bill is an important measure to protect citizens and some of the businesses in major cities.

"I'm hopeful that in the end we'll see the bill pass through committee and move on with what it's designed to do," he told CBC News.

New Democrat MP Françoise Boivin proposed changing the bill to include intent to riot as one of the factors in the crime. Richards' bill leaves the wording as anyone who "commits an offence" by taking part in a riot, which the opposition says is too broad.

Richards says he isn't interested in the NDP's amendment, which he says will "gut" the intention of the bill.

The committee will meet again Thursday to continue clause-by-clause review.

Bill would mean up to 5 years in prison

The new provisions would allow for penalties of up to five years in prison or a fine of up to $5,000 for rioters who wear a mask or disguise.

Justice Minister Rob Nicholson announced Sunday that the Conservative majority formally supports the legislation, meaning it is all but assured of becoming law.

The bill would create two classes of offence.

Those who incite a riot wearing a mask "without lawful excuse" face an indictable offence with prison terms of up to five years.

For those "who participate in an unlawful assembly while wearing a mask or disguise to conceal identity," the charge could be an indictable offence or a summary offence.

Under the summary offence, penalties range up to six months in jail and fines up to $5,000.