A 48-hour strike by driving test examiners has led to thousands of tests being cancelled, union leaders claimed.
Members of the Public and Commercial Services (PCS) union mounted picket lines outside test centres across the country for a second day on Tuesday amid claims that examiners are being told to work longer, harder and for no extra pay because of the new tests.
The union said more than 1,000 examiners took industrial action, claiming that only a "tiny proportion" of the usual number of tests have been held.
The Driver and Vehicle Standards Agency (DVSA) said the union's figures were incorrect.
Officials also warned that when the strike ends, there will be a backlog of tests, worsened by an ongoing ban on overtime.
The DVSA said Monday's launch of the new driving test marked a "significant milestone" in its history, helping prepare new drivers for a lifetime of safe driving.
PCS general secretary Mark Serwotka said: "Ministers need to listen to the concerns of DVSA staff who have shown that they won't be bullied and intimidated by tactics of misinformation.
"Now is the time for Chris Grayling (Transport Secretary) to get a grip of this dispute and insist that DVSA management acts in the interests of both learner drivers and its own staff."