The Equality and Human Rights Commission (EHRC) has launched a formal inquiry into the employment and recruitment practices in the meat processing industry in England and Wales.
Evidence obtained by the equality watchdog suggests the meat and poultry processing sector is characterised by low pay, and has become reliant on agency and migrant workers.
The investigation will look into differences in the pay and conditions of temps who undertake the same jobs as employees with permanent or directly-employed status. The inquiry will also consider the wider implications of changes to the status of agency or temporary workers.
The sector employs roughly 40,000 workers in the UK.
EHRC chairman Trevor Phillips said: "We know that there are good examples of companies and employment agencies who treat these workers fairly, but there are concerns about inequality in recruitment and employment practices in other companies and we want to ensure that fair treatment is the norm across the sector rather than the exception."
Jack Dromey, deputy general secretary of Unite, which represents the majority of workers in the sector, added: "This move should send shockwaves through an industry that has been indifferent to the treatment of its workers."
The inquiry will gather evidence over the next six months and then make recommendations on how to make improvements in the sector.