The case has been adjourned while the discussions takes place. The union is seeking an adjournment until Thursday to allow it to compile more evidence, while Metro wants the case heard tonight to prevent disruptions to train services on Wednesday. A lawyer for Metro claimed the first his client heard of the planned "unlawful" action was via a phone call from The Age. "There's been no notice; there's been no discussion," he said. "There will be considerable disruption to a vast number of people if this action is able to progress."

The Metro lawyer suggested the action be postponed, but pressed the matter should be heard tonight if not. A lawyer for the union said the trains that were planned to be taken out of action were a "significant" safety concern. "Not just to our drivers, but to other staff and, in fact, the travelling public," he said. Metro's lawyer said the same trains had been in service for years. The Rail, Tram and Bus Union has taken the severe course of industrial action over two safety-related faults with Metro's Comeng and Siemens type trains, which together account for about 126 of Metro's 200-odd strong fleet.

The first fault relates to a flaw in the new digital train radio system that sometimes makes it impossible for train drivers to communicate with passengers on the public address system; the second to a string of recent explosions that have happened beneath Siemens train carriages. The union issued two directives to drivers on Tuesday afternoon not to operate Comeng or Siemens trains. In a statement Metro said any action taken tomorrow would be "unprotected industrial action". "We will be working throughout the evening and are doing all that we can to avoid any disruption on the network tomorrow," it said. "We advise our customers to check the website for updates throughout the evening and tomorrow morning." The problem with the PA system is unique to Comeng trains, and led to confusion among passengers on a faulty train that stalled while travelling between two stations inside the City Loop on December 29.

A Rail, Tram and Bus Union statement last night said it did not wish to inconvenience passengers but that it believed safety was paramount. "The RTBU stand ready to work toward a genuine solution in the interest of the travelling public," it said. Locomotive Divisional Assistant Secretary, Jim Chrysostomou, said the union was no longer prepared to risk safety for the sake of running a full timetable. "How long can this continue before someone is injured," Mr Chrysostomou said. "We're not going to endanger our members or the public for the sake of running a full service." Metro had been aware of the two faults for several weeks but had not yet taken the necessary steps to fix them, he said.

"We believe it's an imminent threat to our members' safety and we're not prepared to put them in harm's way," Mr Chrysostomou said. The two union circulars, seen by The Age, were to be issued to Metro by the end of the Tuesday. One states: "As a result of Metro Trains' failure to ensure there is no imminent threat to Drivers' safety by providing a physical barrier to prevent serious injury or death by the force and flames of the exploding static inverters on Siemens trains the following will apply; No Driver is to attend a Siemens train with the pantographs raised." A pantograph connects the train to the overhead wires that transmit power, so the circular effectively puts all Siemens trains out of action. The second directive, relating to the older Comeng trains, states that drivers should make sure at the beginning of each shift that the PA system is operating when the pantograph is both raised and lowered and "in the event the PA is not functioning as required in all modes the fault is too booked in accordance with the fault management system (FMS) as a 'Critical' fault".

Mr Chrysostomou said this directive would effectively halt the entire Comeng fleet from running. "Any Driver that is threatened or coerced by management to act outside policy and procedures should contact the Union immediately," each directive concludes. Public Transport Users Association president Tony Morton said removing Siemens trains from the network could result in the cancellation of up to a third of train services. He said independent experts should be called in to assess the safety of trains where concerns had been raised.