Jeremy Corbyn will promise to tackle the culture of late payments which is forcing more than 50,000 small firms out of business every year.
The Labour leader is to brand it "a national scandal" that big businesses were withholding more than £26 billion a year from small suppliers by paying their bills late, according to analysis of Bacs figures by the party.
It follows a Labour pledge to increase the minimum hourly wage to £10 by 2020 as Mr Corbyn attempts to woo voters ahead of local elections next month.
He is also expected to use a speech to the Federation of Small Businesses (FSB) to pledge to cut quarterly reporting for small firms and to create regional investment banks to make it easier for businesses to access finance.
Mr Corbyn, speaking in London on Tuesday, will say: "Cash is king for any business, and big companies are managing their cash by borrowing - interest free - from their suppliers.
"Some of the biggest names in business are holding cash piles that don't actually belong to them.
"It's a national scandal. And it's stopping businesses from growing and causing thousands to go bust every year. It kills jobs and holds back economic growth."
Labour would require companies bidding for public sector contracts to pay suppliers within 30 days and would consider bringing in fines for persistent offenders in the private sector, Mr Corbyn will say.
He will also moot scrapping quarterly reporting for small businesses and curb any increase in corporation tax rates for small firms.
Mr Corbyn will say: "In last month's budget, the Chancellor bowed to pressure by delaying the implementation of quarterly reporting for small businesses by one year.
"That's not good enough. Labour is against small businesses having to report quarterly. It's a burden, a distraction, that will hold entrepreneurs back."