HARARE, Jan. 23 (Xinhua) -- Workers at Zimbabwe's power utility, ZESA Holdings, have threatened to go on strike over pay rise.

The workers are accusing their employer of failing to honor a collective bargaining agreement of 2012 which awarded them significant pay increases.

ZESA is arguing that it is technically insolvent and has no financial capacity to meet the expected salaries.

It has been contesting the collective bargaining agreement since 2012, arguing that it could only do so after increasing tariffs.

"The threatened job action, if it does happen, will definitely have an impact on security of power supplies," ZESA said in a statement on Tuesday.

"It (ZESA) was and remains technically insolvent as evidenced by a net liability of 479 million U.S. dollars, as at December 2017."

ZESA is running obsolete power plants that are failing to produce adequate power for the nation. It plugs the shortfall through imports from South Africa and Mozambique.

However, the power utility is making strides to improve power supplies and will in March this year complete the expansion of Kariba Hydro power station by an additional 300 megawatts.

The expansion project is being implemented by China's Sinohydro at a cost of 533 million U.S dollars. The first 150 MW unit of the expansion project has been completed and started feeding into the national grid in December last year.

ZESA has also struck a deal with Sinohydro for expansion of the coal-fired Hwange Power Station by another 600 MW.