Zambia faces widening strikes, increased state spending that could drive a hole in the budget and greater state involvement in the economy that could increase worries about the course of Africa's biggest copper producer.

The government - in place since September - has angered its political foes with investigations into corruption by the previous administration and may find it difficult to push laws through parliament in the face of an increasingly united opposition.

Investors have also been rattled by a doubling of base metal royalties in the November budget, while frequent power shortages look set to worsen problems for mining companies.

The country's power-hungry mining firms face short supply, with the government estimating generation capacity will not exceed projected demand until 2015.

Erratic rains have delayed the planting of this year's maize crop, the country's staple, raising the possibility of a poor harvest and rising food prices.

Most mining companies concluded negotiations with unions for better pay and working conditions, but the likelihood of disputes remains in other sectors and government departments.

President Michael Sata, who swept to power last year on the back of promises to spread the benefits of mineral wealth, asked unions this month to keep salary demands close to inflation, which slowed to 6.4% last month. After years of what they regard as paltry pay, many unionised workers may target foreign-owned mining firms for more money.

There is concern that strikes may spread beyond mines to other sectors. In line with his strong anti-corruption pledges, Sata has closely reviewed deals done under his predecessor, Rupiah Banda, whom he criticised for allowing graft to proliferate.