Jeremy Corbyn has vowed to take on the City of London if he becomes prime minister, saying finance should be "the servant of industry, not the masters of us all".
The Labour leader called for a "fundamental rethink" of the finance sector and how it is regulated.
He also promised to give the government new powers to intervene to prevent "hostile takeovers".
The Tories said Labour would "end up harming Britain's businesses".
Mr Corbyn has often criticised bankers, and promised a "fundamental shift" in economic policy if he wins power.
In a speech to the EEF manufacturers' organisation, he said his administration would be the first in 40 years - a period which includes 13 years of Labour government - to "stand up for the real economy".
"There can be no rebalancing of our distorted, sluggish and unequal economy without taking on the power of finance," he said.
"For 40 years, deregulated finance has progressively become more powerful.
"Its dominance over industry, obvious and destructive; its control of politics, pernicious and undemocratic."
'Fewer good jobs'
A Labour government, he said, "will take decisive action to make finance the servant of industry, not the masters of us all".
Mr Corbyn pointed to the ongoing attempt by manufacturing turnaround firm Melrose to gain control of engineering giant GKN as a further example of "short-term performance and narrow shareholder value (being) prioritised over long-run growth and broader economic benefit".
Labour would broaden the scope of the public interest test applied to such takeovers, he said.
Mr Corbyn also discussed Brexit, saying businesses needed clarity on market access regulations.
Taking questions afterwards about his party's position, he said "we have to have a customs union" with the EU after Brexit. And while the UK would no longer "automatically" be a member of the EU's single market after Brexit, Labour wanted a "tariff-free trade relationship".
Responding to his remarks for the Conservatives, Exchequer Secretary to the Treasury Robert Jenrick said: "Labour don't know how to handle the economy and would end up harming Britain's businesses, and there would be fewer good jobs for people as a result.
"We are stepping in to make sure businesses play by the rules, after Labour's failure to properly regulate the banks."
At the same EEF event, International Trade Secretary Liam Fox will hail the UK's manufacturing sector, saying the government is already "laying the groundwork" for new trading relationships across Africa and Asia after Brexit.