Nautilus is supporting a member and master seeking damages for her employer's non-payment of maternity entitlements and breach of contract.
The Union is funding the case on behalf of the member, which has resulted in the UK-flagged superyacht vessel M/Y Lazy P, on which she served, being arrested.
After review by French legal counsel engaged by Nautilus, the member is likely to receive a large compensation pay-out due to the employer's refusal to grant her maternity rights in accordance with French law, as well as her employer's failure to declare her employment to the appropriate authorities, and damages for breach of her Seafarers Employment Agreement (SEA).
Nautilus legal director Charles Boyle said: 'This member came to Nautilus following her employer's persistent refusal to pay her full maternity entitlement. Had they chosen to comply, that would have been the end of the matter. However, our French lawyer uncovered other irregularities, being failures of the employer, which have now resulted in the yacht being arrested, as security against the substantial damages being claimed.
'Nautilus would rather have settled that matter without resorting to seizing the vessel. However, when employers and shipowners refuse to respect our members' rights, the only option left is to arrest the relevant vessel to enforce the maritime lien.'
Lazy P was arrested in September for the UK-born member who was a resident of France and captain onboard the vessel. Lazy P was usually employed in La Napoule, on the French Riviera.
The pay dispute arose when the member, then 32 weeks pregnant, was 17 days into her official maternity leave. She had been on continuous service since 2015 the employer and owner of the vessel being Lazy P Marine Ltd.
A review of the case by French lawyer Lionel Budieu found Lazy P Marine had not declared the member's employment to the British or French administrations. Mr Budieu said the employer's behaviour is 'clearly a fault committed in the execution of the employment contract'.
The Nautilus member agreed to follow the French lawyer's advice by claiming a breach of her contract of employment and terminating her contract for the lawyer to then seek authorisation for an arrest warrant for the vessel as a precautionary measure.
Mr Boyle added: 'Since the Maritime Labour Convention, 2006, came into force, there has been much more focus from unions in assisting seafarers to enforce their rights. Nautilus is leading on ensuring that yacht members are fully assisted in this process. The MLC covers social security, which France has extended to maternity rights. We are confident that these arrest proceedings will result in justice for our member.'