A union has told employees of Westminster City Council to refuse to use biometric fingerprint devices for clocking on and off because of concerns about privacy.
Unison, the UK's largest public sector union, also claims it was not consulted before the machines were installed at local offices for up to 200 staff in the council's community-protection department.
Phil Vaughan, the secretary of the Westminister branch of Unison, told the Telegraph the system was "based on mistrust" and that the union would "resist such draconian measures".
Stephen Higgins, the assistant secretary, said: "We simply do not trust the city council to hold this information securely and see no justification for such a scheme."
Dean Ingledew, Westminster City Council's director of community protection, said the technology doesn't store information or scans of fingerprints, so they cannot be passed on to a third party.
"The system mainly applies to members of staff who are street-based and often work alone and late at night, and many say they actually feel safer with this system because if anyone fails to sign in or out, it is flagged up immediately and calls are made to find out where they are," he said.
"We hope to introduce this technology as soon as possible, but this will only happen after a full consultation with staff," said Ingledew.