The bonus had been agreed as part of a 30 May 2012 deal between the government and police that averted a referendum request and ended a work-to-rule strike.
However, the ministry said it would stop paying the bonus according to the 2013-2014 budget implementation act, Police Trade Union boss Radivoj Uroševič told the STA.
The union deems this a violation of the 30 May agreement, perpetrated despite repeated warnings by the police, according to Uroševič.
The union has been in talks with the interior and justice ministries over the officers' demands, but agreement has proved elusive so far.
Uroševič said strike activities would probably start on Friday, though it is unclear what their intensity will be, a work-to-rule or an industrial action as planned by public sector unions for 23 January.
The second of two police trade unions, the Trade Union of Police Officers, said today its decision will hinge on the government's steps in the coming days.