OTTAWA -- Canadian troops who lost a tax benefit while serving in Kuwait say they're being punished for speaking out against the change.

Canadian Armed Forces members working on the mission against the Islamic State in Iraq and Syria say, despite a House of Commons vote in favour of reinstating their tax-free benefit, the 15 people serving at Camp Arifjan still won't be getting their incomes tax-free.

“The feeling is despair at this point,” one soldier, whose identity is being protected, told CTV News. “We haven’t really heard anything and it doesn’t seem very optimistic.”

They also say the military told them to complain to their MPs if they were unhappy -- then, after two of them took that advice, the military started investigating who complained.

The tax-free status is applied to CAF members serving in dangerous places, but a policy change last fall meant some of them lost the benefit.

The troops at Camp Arifjan had argued others posted in Kuwait still had their tax-free status, so the government tried revoking the benefit from an additional 300 people serving in the country. MPs voted in March to return the tax-free status to the military members deployed to fight ISIS.

The government, however, only returned the benefit for those who deployed before the policy change. Treasury Board President Scott Brison extended the benefit to those who deployed to Camp Arifjan until Dec. 18, 2016, but gave the other 300 military members serving in Kuwait until Aug. 16, 2017.

CTV News has learned that more troops will have their hardship and danger pay reduced in June -- those serving in Egypt’s Sinai desert, where ISIS has been expanding.

The tax breaks, worth between $1,500 to $1,800 per month, are provided to military members who meet certain criteria related to the risk of their duties and the relative hardship of their living conditions while deployed overseas.

'Order seems vindictive'

When the military members pursued the disparity, they were told they got an extension on the benefit, "so that is that," an officer in Ottawa wrote in an email provided to CTV News.

"Non-grievable through the CAF system. But if anyone thinks they have been hard done by (still), then I suggest they use their member of Parliament," the email said.

Despite that response, some of the troops told CTV News that the military started questioning them to find out who emailed the MPs.

"Surely the Government of Canada can afford to treat the soldiers in Arifjan fairly. There are after all, only 15 of us," one person said in the email to MPs.

The minister, the military member said, recognized that the level of hardship is the same for all members serving in Kuwait.

"It is clear we all share the same conditions but are to be paid very differently. On the face of it, the order seems vindictive," the soldier wrote to MPs.

In another email, the CAF member said it's "unfathomable" to provide different benefits for members posted an hour's drive apart.

"Those in Camp Arifjan apparently are the target of their own government. How sad is that?" the troop wrote.

'You can't tell me that he is going to be safe'

One woman whose son is serving at Camp Arifjan says it's not right they be told they can't complain to MPs.

"He should have freedom of speech just like any other Canadian citizen," the woman said in an interview with CTV News. "Why does he lose his rights as a Canadian citizen because he's military? No."

The initial decision to cancel the tax benefit wasn't fair, she argued.

"Any mission, in any of those countries, in any country that isn't this one, is dangerous," she said.

"You can't tell me that he is going to be safe. You can't tell me that they can protect him in a country that is volatile."

Defence Minister Harjit Sajjan says the government has tried to address the immediate issue and that he's directed Chief of Defence Staff Jonathan Vance to look at the whole compensation package.

"We want to make sure that we look at the thorough problem and not just have another piecemeal fix and come into another problem down the road," Sajjan said Wednesday in Ottawa.

"We're doing a thorough review on this - [the] chief of defence is working diligently on this and I look forward to announcing that as well."

With a report by Mercedes Stephenson