A safety recall by five different car manufacturers is at the centre of missing data involving the Driver and Vehicle Agency in Northern Ireland.
The drivers' details were on two discs
The agency lost two discs containing the details of 6,000 people after they went missing en route to Wales.
The data was being provided in response to a recall by Fiat, Vauxhall, Citroen, Alfa Romeo and SSangyong.
The missing data includes details of 7,685 vehicles and more than 6,000 vehicle keepers.
The data includes the keeper's name, address, registration mark of the vehicle, chassis number, make and colour.
Cars involved in recall
Fiat - Ulysse, Scubo, Doblo
Vauxhall - Corsa
Citroen - Rhythm, Airplay, Exclusive
Alfa Romeo - Spark, Sport, JTD, JTS
SSangyong - Rodius
However, the DVA said no personal financial data was on the discs.
Northern Ireland Assembly Environment Committee chairman Patsy McGlone said full details needed to be disclosed.
"I am seeking clarification from the Department of the Environment as to why were these companies asking for details of the cars, what were the defects and has the department sought further detail from the manufacturers that these are not defects which could be potential road safety issues?" he said.
On Wednesday, the head of Northern Ireland's Driver and Vehicle Agency said drivers' details "should not have been posted the same day it was revealed 25m people's details were lost".
Brendan Magee, head of NI's said he would now "clearly have to look" at his own position.
They were sent the day it was reported 25 million child benefit records went missing in the post.