The former MP, already under pressure over some aspects of his personal circumstances such as his wealth and sending his children to private school, defended his family firm in a combative BBC Radio Scotland interview.
Mr Sarwar, who is challenging Richard Leonard for the vacant leadership role, urged people to respect a private decision made at home in consultation with his wife.
The Glasgow MSP grew increasingly irate with presenter Gary Robertson, accusing the Good Morning Scotland host of pursuing personality over politics when he was asked if he was in fact ‘one of the few’ - a play on Labour’s slogan to work for ‘the many, not the few’.
Mr Sarwar owns around a quarter of the shares in United Wholesale Scotland, which operates a chain of cash and carry and groceries stores across the country.
It was revealed that the company has no formal Trade Union recognition, and pays less than the ‘real’ living wage of £8.45 which is endorsed as part of Scottish Labour policy.
Asked about influencing his family business to transition to the real living wage, Mr Sarwar said that the wage is voluntary.
He added: ““One, I’m a minority shareholder in the company.
“Second, I have no role in the company. I’m not a director in the company. I have no say in how the company operates.
“But I have had assurances from the company that they do want to transition to a real living wage for all employees.”