VANCOUVER -- The federal government’s list of banned firearms continues to grow and that’s catching some gun owners and sellers by surprise.

Maple Ridge gun dealer Matthew Mendel had to pull a lot of stock from the shelves at Wanstalls Hunting and Shooting recently when the government added 1,500 weapons to the prohibited list.

“I’m assuming because it has a pistol grip and an adjustable butt stock is the reason why it made it on the list,” he said as he held a semi-automatic shotgun.

But that gun wasn’t among the 1,500 weapons banned with much fanfare May 1 in the wake of Canada's deadliest mass shooting.

Instead, the semi-automatic shotgun was quietly outlawed in the middle of the month.

“Other firearms have been prohibited without any notification to the people who own them or businesses,” Mendel said. “So RCMP is going through the Firearms Reference Table and making those firearms prohibited and not notifying anyone.”

Mendel’s store carries several hundred different varieties of firearms and staff say without proper notification, the onus is on them to check the prohibited list every day to make sure they’re not breaking the law. The RCMP, which oversees the list of allowed and prohibited weapons, says it is working through the list and re-classifying some guns based on the new criteria brought in by the government.

“The Canadian Firearms Program is working as quickly as it can to ensure that these classification determinations are completed and that any changes be published in the Firearms Reference Table,” the Mounties said in a statement.

“All we want to do as responsible gun owners is make sure we’re not selling prohibited items without knowing it,” Mendel said about the reason he wants a better notification system in place, adding that many collectors and sport shooters are also likely unaware some of their guns are now illegal.