Proposals to cut up to 24 posts in the region and lose one fire engine from the Wrexham station are up for consideration at a meeting on 20 June.
North Wales brigade secretary Shane Price said: "The service has already suffered heavy cutbacks in staffing."
Deputy Chief Fire Officer Dawn Docx said there are a variety of money saving options on the table.
The Wrexham station currently has three engines.
The FBU's Mr Price said he felt the authority has failed to take into account how much support crews in Wrexham offered to surrounding fire stations like Johnstown and Chirk.
But Mrs Docx said the fire service's budget could no longer be frozen due to the cost of inflation and rising pension costs and the decision to reduce future services was "the least damaging option".
The authority's executive members met with senior fire officers in May to discuss future plans.
She said: "The working group had come to the conclusion that the option that they intend to explore further and consult on, would be the potential removal of a whole time pump from Wrexham by the end of this decade.
Once the full authority has agreed on its proposals there will be a full public consultation later in 2016.
The Fire Brigades Union has warned against "brutal cuts" being considered by the North Wales Fire Authority.