Anas Sarwar was forced to defend the wages paid at his family’s firm in a bruising BBC exchange.
The Scottish Labour leadership candidate, who sends his children to private school, faced claims he was “one of the few”, in a reference to his party’s slogan.
Mr Sarwar said not everyone was paid the real living wage of £8.45 at United Wholesale because it is “voluntary”.
The Glasgow MSP, who is up against Richard Leonard in the contest, is said to have a stake worth millions of pounds, but is not a director and has “no say” in how it runs.
In a BBC radio interview he was asked whether his decision to send his children to private school, as well as his involvement in United Wholesale, meant he was “one of the few”.
The Scottish Labour slogan is “for the many, not the few”.
“No I don’t accept that at all,” Mr Sarwar replied.
“The reason why I am in the Labour Party is because Scotland has cradled my family, it has nurtured my family, it has given it success.
“The reason why I am in the Labour Party is because I don’t choose to opt out of politics, I choose to fight for equality and fight for opportunity.”
Mr Leonard, who is on the left of the party and a strong supporter of Jeremy Corbyn, has received the backing of Scotland’s largest union Unite.
A majority of Labour MSPs are expected to support Mr Sarwar, who is a centrist.
