Hundreds of workers at sports retailer JJB have gone on strike in a dispute over pay and conditions.
Workers are manning picket lines outside the firm's Wigan base
Staff at the firm's warehouse in Wigan, Greater Manchester, are striking for 24 hours for the third time in two weeks.
The GMB union said workers are mounting picket lines throughout the day and outside JJB sports shops across England and Scotland on Saturday.
GMB officials have also complained that employment agencies illegally supplied staff during last week's strike.
Regional secretary Paul McCarthy said the union was completely dissatisfied with the Employment Agencies Standards Inspectorate for failing to enforce the law and take action against the agencies involved.
A number of union members will travel from Wigan to protest outside the Inspectorate's offices in London.
They will hand in a letter giving details of agencies the union claims had illegally supplied staff.
Mr McCarthy said: "These are low-paid workers on the national minimum wage, and the activities of the employment agencies in supplying strike-breaking staff is prolonging the dispute."