The union representing more than 20,000 Alberta government workers says contract negotiations are getting off to a difficult start especially with the critical issue of filling vacant positions coming to the forefront.

The Alberta Union of Provincial Employees is seeking pay raises of four and five per cent over the next two years after its last contract expired at the end of August.

When that deal was signed in 2007, the economy was booming and the workers received almost a 15 per cent pay hike over the life of the agreement. Now the provincial government wants a pay freeze.

Union president Guy Smith said the union is also concerned about positions that haven't been filled because of a hiring freeze.

Smith said staff shortages have been building since the last deal was ratified.

"Even during that time there were staffing issues that weren't addressed and I think it's just come to a head now that folks after years and years of experiencing that lack of staffing levels they're at their wits end and we have to deal with that at the negotiating table," Smith said.

Lloyd Snelgrove, president of the Alberta treasury board said the government will hire staff in some areas where it may be stretched too thin but said hefty pay raises and a hiring bonanza are not likely.

More contract negotiations are scheduled for later this week.

With files from the CBC's John Archer