Milford Haven Port Authority launched a High Court bid to try to stop pilots and launch crew members from walking out on Thursday and Friday.
Mr Justice Sweeney has ruled that notices of industrial action issued by the Unite union did not fully comply with the relevant legislation.
The dispute centres on changes to the staff pension scheme.
Delivering his ruling a day after the hearing in London, Mr Justice Sweeney said that the “balance of convenience” favoured the port authority.
Talks between the port authority, the union Unite and the conciliation service Acas are continuing.
The port authority argues that it must alter its final salary pension scheme because of a huge deficit which it says is growing and unsustainable.