A stop-work meeting involving some Public Transport Authority staff is expected to disrupt off-peak train services today.
Transperth advises passengers to avoid train travel in the middle of the day.
PTA managing director Mark Burgess said a small number of staff, including some working in the safety critical Train Control area, had indicated an intention to attend a meeting at noon.
Train operations may be affected between about 10.30am and 2.30pm, but should be back to normal in time for the afternoon peak.
Mr Burgess said the PTA was "very disappointed" by news of the possible disruption.
"The Public Transport Authority works hard to deliver reliable and efficient rail services and this action directly undermines that," he said.
"We hope there will be no stoppage, but are conscious of the need to warn our passengers as early as possible that there is a chance services will be disrupted.
"We are currently in EBA negotiations and yesterday obtained an order from the Industrial Relations Commission instructing the staff at their posts, however, we believe they intend to ignore the order."
Mr Burgess said it was yet clear how many people would attend the stop-work meeting, or the full extent of the impact on train services.
"However, given the uncertainty and the short notice provided to us, it is important we advise the public of this possible disruption," he said.
"We are doing everything we can to keep the disruption to a minimum; for example, we have already started work to try and arrange as many replacement bus services as possible.
"Fortunately we are in the school holiday period so there will be a few more buses available to transport people during the day than there might have been during the school term."