WORKERS in a dispute with public transport operator Nexus are threatening strike action which could cause chaos on the Metro system.

Unison members have rejected a move by Nexus bosses to introduce job evaluation, linked to a new performance-related pay scheme for 450 staff, and have agreed to ballot for industrial action.

Anger has also been expressed over plans to extend drug and alcohol testing to all of the 1,050-strong workforce. At present, tests are restricted to safety-critical staff, including drivers, track and depot workers.

Any industrial action, if taken, could include key workers such as control room staff, responsible for train movements and overhead lines.

When controllers threatened to walk out last year in a pay grading row, Nexus drew up contingency plans to keep the trains running.

There was also a warning last night that the Rail, Maritime and Transport Union, which represents 350 Nexus drivers, engineering workers and other grades not directly involved in the scheme, may also become involved in the dispute.

Under the proposed scheme, staff would qualify for extra money on top of their annual pay award. This could add up to 7.5 per cent to wages, but union leaders say conditions of service will be eroded.

Nexus management said the deal would benefit the vast majority of staff and said they hoped a strike could be avoided.