Mohammed Riaz, 63, of Manchester Road, Nelson, Lancashire denied forcing or compelling Margorsha Bienick and Michal Czesniawski into slave labour.
The jury was unable to reach a majority verdict after six hours of deliberation and was discharged by the judge at Burnley Crown Court.
The prosecution is yet to decide whether a retrial will go ahead.
Mr Riaz Snr faced two charges under the Modern Slavery Act 2015.
His son Khuram Riaz, 27, was cleared of similar charges earlier in the trial.
A jury has failed to reach a verdict in the trial of a man accused of forcing a Polish couple to work for £4 a day.