The Liberal government has broken a promise to immediately implement firearm-marking regulations to help police trace guns used in crime.

On the eve of the Trudeau government's Friday milestone of 100 days in office, the pledge had not been fulfilled.

Just before the August federal election call, the Conservative government quietly published a notice deferring the firearm-marking regulations until June 1, 2017 — the seventh time the measures had been delayed.

The regulations would require that specific, identifiable markings be stamped on firearms and had been slated to take effect Dec. 1 of last year.

The July 29 notice from Public Safety Canada said the delay would allow the government to continue consultations, despite six previous delays in enacting the regulations, first drafted in 2004.

In their election platform, the Liberals said they would "immediately" implement gun-marking regulations. The party also promised other, longer-term measures aimed at making it harder for criminals to get and use handguns and assault weapons.

The marking-regulation promise is also listed in a briefing book document prepared for the prime minister entitled "Key Commitments for Action in First 100 Days."

The office of Public Safety Minister Ralph Goodale did not provide a requested update on the marking initiative.

The long-planned regulations would require domestically manufactured firearms to bear the name of the manufacturer, serial number, and "Canada" or "CA." Imported guns would have to carry the "Canada" or "CA" designation along with the last two digits of the year of import.

The measures would help Canada meet the requirements of the United Nations Firearms Protocol and a convention of the Organization of American States.

There is support among police for the marking scheme in order to expedite investigations into gun crimes and detect firearms trafficking, smuggling and stockpiling, the Public Safety notice says. The import markings can also help law enforcement determine whether to focus on a smuggling operation.

"Tracing can offer early investigative leads, contribute to cost efficiencies for police by simplifying efforts, focus investigations given that time is critical to solving crimes, and help to build a strong evidentiary case to obtain a conviction," the notice says.

Some firearms advocates have argued the obligation to mark imported guns would mean acquiring marking technology or making arrangements for another company to apply markings, with an estimated cost of $200 per gun, the notice says.

However, an independent study commissioned by the government said the cost to stamp or engrave markings for Canadian manufacturers and large importers would range from nothing at all to $25 per firearm. It was not possible to gauge the impact on individuals and small importers.

The Coalition for Gun Control argues that marking is an essential tool for enforcement, helping states in their efforts to trace weapon flows and preventing diversion of legal guns to the illicit market.

The National Firearms Association disputes the notion that markings help police solve crime and would like to see the entire plan cancelled. Imposing the marking requirements would put an undue financial strain on businesses, the association says.