Workers at three liquor distribution centres in British Columbia were on the picket lines Tuesday in the first of what could be a series of walkouts by the province's largest public-sector union as it presses for higher wages.

The one-day strike by members of the BC Government and Service Employees Union targeted three liquor distribution centres in Vancouver, Victoria and Kamloops, although only one government-run liquor store, in Vancouver, was closed to the public because of the strike.

The dispute comes as B.C. continues to insist new collective agreements must not cost the province any additional money -- a policy that is likely to hamper negotiations with other public-sector workers and further strain relations between the government and its unions.

The strike centres around contract negotiations for more than 25,000 members of the union, which is negotiating a collective agreement to replace one that expired at the end of March. The workers include sheriffs, probation officers, social workers and liquor store and warehouse employees.

Negotiations headed to mediation, but those talks broke down last month, said union president Darryl Walker.

"We want to identify to the public that we are not happy with the wage offer that has come from the provincial government," Walker said in an interview Tuesday.

"They haven't had a pay raise since 2009 and are basically falling further and further behind," he said of his union members.

The union hasn't indicated yet whether it will stage any additional walkouts in the coming days or weeks, or which workers would take part.

The main issue in the dispute is wages, and both sides are proposing two years of pay increases.

The province has offered the union a two per cent wage increase in the first year of the contract and 1.5 in the second, said Walker, although that proposal doesn't take effect until this month, rather than when the previous contract expired three months ago.

The union, on the other hand, wants 3.5 per cent in the first year and a cost-of-living increase in the second.

The workers' most recent contract was negotiated under the province's so-called "net-zero" policy, which said any pay increases must be offset by concessions elsewhere in a collective agreement.

For the current round of public-sector bargaining, the province has revised the policy slightly and given it a new name: "co-operative gains." Workers can negotiate small wage increases if they can identify equivalent savings in their ministry's budget.

Walker said the union is playing by those rules, putting forward proposals to make the government more money to help pay for wage increases. Those proposals have included opening government liquor stores on Sundays and expanding sheriffs services.

Finance Minister Kevin Falcon couldn't be reached for comment, but he has defended the Liberal government's bargaining strategy and said the most recent offer for the government workers' union was the best they could hope for.

Falcon suggested that if workers went on strike, the province's next offer would be worse, not better.

The current fight could foreshadow negotiations with other public-sector workers, with more than a quarter-million union members negotiating contracts this year.

The BC Government and Service Employees Union alone represents roughly 65,000 workers and the dispute behind the liquor store walkout only involves a portion of them. The more than 25,000 union members involved in that round of negotiations are those who work directly for government ministries and Crown corporations.

Walker said one reason the province's Liquor Distribution Branch was targeted first is the government's plan to privatize liquor warehousing and distribution.

The government announced the plan in its budget earlier this year and is currently in the early stages of selecting a shortlist of potential bidders.

"We think that's wrong," said Walker. "We think privatization of the system is going to cost people in the long run. It will probably cost the province revenue. There's no business plan for why this decision was made."

The finance minister has previously said that it would only proceed with the privatization plan if the final proposal saves the government money.

The initial request for proposals closed last week, and the province announced Tuesday that six companies have submitted packages: ContainerWorld Forwarding Services Inc., Exel Canada Ltd., Hillebrand Westlink Inc., Kuehne and Nagel Ltd., Metro Supply Chain Group Inc. and Schenker of Canada Ltd.

An evaluation committee will narrow that list down to three by July 20. The winning bid is expected to be announced in October, with a contract finalized by March 2013.