London Underground workers may go on strike over plans to introduce staff identity cards, unions have warned.
The proposals could see up to 8,000 Tube workers, including engineers and maintenance staff, issued with ID cards.
The RMT union said the new system could be used to check hours worked by staff.
But Metronet and Tube Lines, which maintains the network, said the card would be used to check workers’ licences and would improve safety.
The RMT’s London regional organiser, Bobby Law, warned that if the plans went ahead without agreement there would be a ballot for industrial action.
Metronet said talks were continuing and no decision had been made as to whether the card would include any biometric features.