The comments, from the Vehicle and Operator Services Agency section, came as Dft published the revised fees for Heavy Goods Vehicle and Public Service Vehicle operator licences.
The new fees, which come into effect on April 1, will see operators using non-VOSA sites pay 4% less than those using VOSA test facilities.
On behalf of the union's 500 VOSA members Prospect negotiator Helen Stevens said: "Where is the overall strategy, a vision for safety and testing? Creating a differential between testing facilities, making non-VOSA sites more financially attractive, is part of a continual attempt to drive operators away from their local VOSA-owned stations.
"This is simply robbing Peter to give to Pauline regardless of the possibility that Peter and Pauline together could do a better job. Without planned provision of testing sites to support the industry we are concerned that short term solutions will damage the long term effectiveness of the national provision – and that means less safe roads."
"While VOSA chief executive Alastair Peoples has described the differential as moving 'further towards charging the full cost of VOSA facilities to those who use those facilities,' he fails to mention that many authorised test facilities operators charge pit fees and for ancillary things such as the loading of vehicles for brake testing which are included in the VOSA test fee.
"Operators facing those additional charges will discover they far exceed the small saving from visiting a non-VOSA site. This is not, as Peoples says, about providing an 'even more attractive option,' for the industry, but about reinforcing the principle of a different fee regime until the gap between facilities prices VOSA sites out of the market."