Who is responsible
It will be interesting to hear from a legally qualified chap on here but, as a layman, whilst previously managing companies I always considered the company to be responsible for an employee's actions whilst performing their employed duties. This is why retail companies are held liable when check out operators are rude to customers or make sexist or racist remarks. I would expect the company to prosecuted for the payment of the fine, then internal disciplinary actions within the company are a different matter. However it may be illegal under employment law of the country where the person is employed for money to be deducted from their wages without their consent.
Either way I think the pilots concerned will probably be looking for a new job.
MM