Aontú leader Peadar Tóibín has labelled the NCT's plan to go cashless as a "terrible decision", adding that it should be reversed.
The car testing services has confirmed its plan to go cashless in the "coming months", while drivers will have to pay in full in advance of their test.
Payment will be available online or by postal order.
"it's a terrible decision by the NCT and it should be reversed," Mr Tóibín told Newstalk. "Cash is the most inclusive way to pay for items."
He added: "It means that people - no matter what their age or their skill level, no matter if they've access to the internet or smartphones - that they have the ability to participate fully in society.
"Cash is recognised to be crucial, especially for the inclusion of vulnerable citizens."
He said cash options were also important for older people.
"The many older people who can't use smartphones or don't have access to the internet, for example, would have to ask their children for help or ask their neighbours for help.
"When a person is older what we want to do is actually strengthen their autonomy, to strengthen their independence.
"By getting rid of cash, this has the opposite effect."
