Strike action targeting Sydney train commuters in recent months is set to extend to the Upper Hunter.

Passenger trains will not run on the Upper Hunter and Hunter lines on August 23 between 10am and 4pm.

Disruptions in the Upper Hunter are likely to be longer because of the time it will take to restart services.

Rail staff are angry over train safety issues and stalled pay negotiations.

Rail. Tram and Bus Union New South Wales Secretary Alex Claassens said the safety of passengers is at stake.

Image: Darren Cutrupi