They are driven to arrive on the front lines of a war that is not their own for a variety of reasons: frustration with what they call Canada’s inadequate military response, anger prompted by grisly beheading videos and stories of brutal treatment at the hands of ISIS.

For some of the Canadian military veterans who have volunteered to join the Kurdish battle against the Islamic State in Iraq and Syria, it is also about relieving boredom that has descended since their last battles in Afghanistan.

The volunteers will not be paid, so they are not mercenaries. But their decision to join up does present a host of potential problems — legal and practical — for Canada.

The idea has attracted a less-than-enthusiastic response from the chief of defence staff, Gen. Tom Lawson.

"I do not encourage Canadians to leave our nation and to head to other nations to get involved with the militaries" of those nations, Lawson said.

One Kurdish force, The Lions of Rojava, uses photos like this on its Facebook page to recruit Western volunteers to join their fight against ISIS. (Facebook) That echoes warnings made by the British government urging people not to go and join the fight themselves. It said they could face charges.

In a statement, the Home Office said: "Fighting in a foreign war is not automatically an offence, but will depend on the nature of the conflict and the individual’s own activities."

So far, Canada has only issued a general travel warning, advising people not to go to the region for any reason.

Problems loom

But a professor of international law at the University of British Columbia, Michael Byers, said the presence of Canadian veterans fighting with Kurdish groups poses possible complications.

“There are two issues here: whether they can go and the second issue is how they behave when they get there,” said Byers, author of War Law, a book on the laws of war.

Travelling to the region is perfectly legal, said Byers. It gets more problematic when the volunteers go into battle.

Kurdish forces have been accused of violating international law. On more than one occasion, they have presented prisoners to journalists to be interviewed on camera. That is a violation of the Geneva Convention.

It emerged several weeks ago that Gill Rosenberg, a Canadian-Israeli, had become the first female foreign fighter to join the Kurds fighting ISIS. (Facebook) A Dutch news team also reported that Kurdish troops had executed prisoners, also a violation of international law. A Kurdish commander denied the claim.

One Canadian veteran of the Afghanistan war who is preparing to go and fight with Kurdish forces said he would have to report any such violations if he witnessed them. Still, it was not clear to whom he would report.

"You know, you cannot be going around like a cowboy shooting everything," said the veteran who did not want to be identified. "You have got to be responsible, professional and follow the guidelines — the laws of war."

His concern reinforces the problem highlighted by Byers.

“Anyone who goes over there to fight should be aware that they are subject to Canadian and international jurisdiction with regard to the laws of war.”

There is another issue: one of the Kurdish fighting forces, called the Kurdish People’s Protection Units or YPG, is linked to the Turkish-based Kurdistan Workers Party, known as the PKK.

It is considered a terrorist organization by the Canadian government, raising the possibility that Canadians could end up violating anti-terrorism laws.

Lawson had one more warning for Canadians who seem to eager to sign up.

“Be very careful. You are swimming with the sharks and there is no safety net.”

There are additional concerns about how the volunteers' presence could complicate Canada’s official military operations. If a Canadian gets into trouble, is captured or injured, would Canada be obligated to stage a rescue mission?