Asda has been accused of forcing workers to choose between caring for vulnerable relatives or losing their jobs.
Union chiefs claim staff have been threatened with the sack if they refuse to sign a new “flexible” contract that cuts paid breaks and reduces holiday entitlement.
The GMB say 13,000 Scots employees face being affected.
One Scots worker said she relies on regular hours to care for her disabled son and husband.
The mum added: “If Asda forces me on to the new contract, I’m worried I will have to leave so I can look after my family.”
An Asda spokesman said the contract will increase the pay of more than 100,000 workers, adding: “We don’t want any colleagues to leave.”