The Health & Other Services Personnel Trade Union of South Africa (Hospersa) has declared a dispute against SANParks following months of protracted wage negotiations.
A spokesperson Kevin Halama says two other unions are joining their dispute to negotiate for better working conditions.
He says if the dispute remains unresolved, unions could bring all facilities to a grounding halt, which would have a negative impact on tourism and conservation efforts.
Parties reportedly deadlocked after all recognised unions rejected SANParks' final wage increase offer of 5,5% and have demanded an 11,5% wage increase.
The unions have now referred the matter to the Commission for Conciliation, Mediation and Arbitration (CCMA) for conciliation to try and end the impasse.
Should the conciliation remain unresolved, a certificate of outcome declaring that unions can embark on industrial action/strike as the next course of action will be issued by the commissioner.
Halama says the three unions have about 5 000 members.