Although Zambians may have been expecting their president's death it has nonetheless left many in a state of shock.

Driving through Lusaka I'm struck by a terrible contrast. There are full-page photos of Michael Sata under headlines announcing his death on the cover of every newspaper. They're carried by salesmen who dodge cars at intersections as they expertly weave through the traffic with one eye on the ever-changing signal lights.

But in the background are posters and banners marking the country's 50th year of independence from Great Britain. Zambians commemorated the Golden Jubilee last Friday. That such a celebration should so quickly be followed by national mourning seems cruel.

Davy Chiyobe, the president of the Civil Servants and Allied Workers Union of Zambia, says "a dark cloud has descended on us", before urging all citizens to mourn with hearts full of love and peace. He says it's customary for people to put aside their differences when someone passes away. That people should do so in Sata's honour.

But the mourning period promises to be brief in comparison to the pressing business of choosing a new president that will consume the country over the next three months (the time within which the constitution stipulates a presidential by-election should be held).

Soon Chiyobe will take up the workers' fight again. His members are angry at a two-year wage freeze imposed on civil servants by Sata's government. They were told there simply isn't enough room in the budget for any pay rises as the money was being put towards infrastructure development instead.

The union was threatening to hold a nationwide protest a week after the Golden Jubilee. All that's on hold, for now. But it was clear when we spoke that he's determined to take on the new president and government as soon as his union deems it appropriate.

He argues that development isn't just about roads and bridges, it's also about investing in people by giving them fair pay rises - money they can re-inject into the economy. The race to be president will be hotly contested but whoever wins will have to be prepared for the demands of thousands of civil servants who think they've been given a raw deal.