Each party is required to bear their own costs in relation to a FWC matter (section 611) thus you are not liable to pay the costs incurred by your employer.
The costs you must bear include the application fee of $68.60 and your own legal costs incurred, if any.
However you or your employer may be ordered to pay some or all of the costs of the other if your FWC application or response:
You will not be required to pay the fee if the FWC is satisfied that you will suffer serious hardship if you are required to pay the application fee of $68.60.
You must apply to have the application fee waived at the time you lodge your FWC application.
You must complete a separate Fee Waiver form available.