A concession the Wellington City Council probably won't be able to implement the living wage for all its contractors.

This follows the council's decision last night to adopt the living wage for those working under the regional security services contract against the council's own legal advice.

Councillors voted nine to six in favour of the change.

Deputy Mayor Justin Lester said the legal advice referred to a blanket policy towards the living wage for all contractors.

But he said the council has agreed to work on this on a case by case basis.

"I'm not saying now hand on heart that we could definitely do the full contract. We probably can't, the costs are likely too high."

Lester was one who backed it, pointing to how little the living wage has impacted council in the past.

"We introduced the living wage for all 400 or so of our internally employed staff years ago. What happened?"

Chief executive Kevin Lavery has warned council about the legal challenges it could face, and says the policy puts him in a difficult situation.

"I would have a problem directing one of my employees to implement something I know to be potentially unlawful, that's because I have a duty as a good employee and I take it seriously. You have that same duty to me as your CEO.