The case centred on three scaffolders who were denied employment by Interserve on a Murco oil refinery shut-down job.
The trio claimed they were denied work because of their trade union activities and that their names appeared on a blacklist.
Those claims were thrown-out at a hearing earlier this year. And the tribunal rejected an appeal by the men last week.
The tribunal heard that a Unite official had asked for the trio to be taken on as shop stewards.
But the Interserve manager concerned regarded the move as a form of bullying and refused to be dictated to by the union about who the firm should employ.