The City of Calgary may have to spend more than $15 million to help small business property owners with hefty property tax hikes this year.

Last year, council voted to reach into savings to protect non-residential property owners outside the core with large tax hikes due to a shift in the tax burden away from downtown.

"Council overwhelmingly supported the need to be able to cushion people this year who have been hit by the assessment shift and I have not heard anything from my colleagues on council that would indicate they are softening on that," Mayor Naheed Nenshi said.

Downtown property values fell by $4 billion last year, which resulted in the substantial tax hikes for businesses outside the core.

The rising vacancy rate in office towers is directly linked to the drop in downtown property values.

Nenshi said council may have to look at helping more than just small business property owners, as large property owners are also affected and they directly pass on the costs to small businesses who lease space from them.

"A lot of the very large property taxpayers are landlords that have a number of small businesses in their locations. Because of the way net leases work, the property taxes are flowed through, we would not capture all small businesses if we only look at small business asset value," Nenshi said.

"As I've said before, this is devilishly complicated stuff."

Details on how the assistance will be doled out are expected to be announced next week.