Last month Transport for London made it compulsory for children using the network to carry Oyster photocards. This has raised concerns about the amount of data the company is collecting.
Parents and the Information Commissioner are not pleased with the changes. The ICO is asking TfL why it is collecting so much data on young people, what purpose such data will serve and how long it will be kept for.
The Zip card is compulsory for 11 to 15 year olds and can also be used by some 16 to 18 year olds. Children aged between five and 10 who travel unaccompanied will also need a Zip card.
Transport for London said it needed the information in order to prevent anti-social behaviour.
Rachel Rolfe, a mother who objects to the scheme, told the BBC: "I don't think that children need ID cards, once your information is out there you can never get it back. And I think you can't protect it."
The ICO said it had serious concerns about the scheme and was contacting TfL for clarification.
A spokesman for TfL told The Register: "We take data protection extremely seriously and information is not passed onto third parties except the company which makes the cards. We are happy to discuss this with the ICO." The application process collects the child's name, date of birth, address, school and telephone number.
There are now 413,000 cards in circulation. TfL received 753 complaints about the scheme between 1 and 19 June, mostly to do with lack of awareness rather than data protection concerns.
Of course for the paranoid adult, or the child who doesn't mind paying, you can still get an anonymous Oyster card. ®