Jeremy Corbyn has called for business reform after the collapse of BHS, which has several stores across the North East.
The Labour leader wants it to be mandatory for employers with more than 250 staff to bargain collectively with unions.
Writing in The Observer he said it would be the best way to guarantee fair pay.
Mr Corbyn, who is facing a leadership challenge from Owen Smith, blasted zero-hours contracts and record levels of poverty among those in work.
Even new Conservative Prime Minister Theresa May knows she has to "pay lip service" to corporate reform, he said.
After highlighting the examples of unions who have won better conditions and pay for their members, he said: "But the best way to guarantee fair pay is through strengthening unions' ability to bargain collectively.
"That's why it should be mandatory for all employers with over 250 staff to bargain collectively with recognised trade unions."
Mr Corbyn also criticised the former owner of BHS Sir Philip Green, saying he had "asset stripped the company" and "left the Government to pick up the pieces".
He said: "The former BHS owner will never know the insecurity faced by his ex-employees or millions of other workers legally exploited by bad bosses."
Labour has set up Workplace 2020 - an initiative to formulate a new business settlement to benefit workers and employers - and is committed to strengthening union rights and reforming company law, he said.