The Australian Services Union has added its voice to calls for a higher car expenses allowance for NDIS workers.

The Australian Council of Trade Unions has made an application to the Fair Work Commission to increase the amount community and disability sector workers can claim for fuel expenses when driving their own car for work.

The ASU says NDIS workers are struggling to afford fuel to drive clients to essential appointments, with some being left out of pocket.

It says the government's initial fuel excise cut was welcome, but was not enough to shield disability workers from high prices.