Former Greek Prime Minister Alexis Tsipras has pledged to abolish an annual flat tax on businesses and to scrap rules that tax the self-employed on presumed rather than actual income.
The proposals are an overt bid for the support of business owners ahead of national elections next year.
"A left that wants to take on responsibility cannot be hostile to entrepreneurship," Mr. Tsipras told a gathering of young entrepreneurs and professionals in Athens.
He drew a sharp line, however, between companies that invest and innovate and those that he said gain an edge through tax evasion and political connections.
Mr. Tsipras now leads the Greek Left Alliance, or ELAS.
He said his party would tax the self-employed on what they actually earn, backed by effective audits.
He also proposed a new 120-installment plan for repaying tax and social security debts, with penalties written off, and promised to cut energy costs by up to 30%.
At the center of his economic plan is a "Convergence Fund" of 3 billion euros ($3.5 billion) a year.
He said it would leverage about 25 billion euros in investment over four years to narrow Greece's gap with average European living standards.
Mr. Tsipras accused the government of strengthening cartels and leaving small businesses without financing. He also said Greece had squandered the European Union's pandemic recovery fund.
The government defends the presumed-income rules as a pillar of its crackdown on tax evasion. It says the crackdown will bring in 9.1 billion euros in extra revenue from 2024 through 2027.
A Marc poll this week put ELAS in second place with 15.8%, well behind the governing New Democracy party at 30.5%.