Transport for Wales services were cancelled on the line on Tuesday morning and the rail operator says disruption is expected until the end of the day.
TfW has advised that services between Swansea and Shrewsbury via Llandrindod have been suspended and that they regret that replacement road transport is not available.
The train operator is also seeing continuing cancellations because of a number of trains needing to be repaired at the same time.
The company's advice is to check before travelling on services between Aberystwyth and Shrewsbury.
"Some services will not operated between between Aberystwyth and Shrewsbury," a company spokesman said. "Please check before travel."