Scottish Power has been accused of "unfettered profiteering" after the privatised energy giant raked in £924.6 million in profits during the first six months of the year.
Unite said the company - which is owned by Spanish conglomerate Iberdrola - was an example of trickle down economics at its worst.
It comes as the cost of electricity and gas has soared in the past 12 months - plunging thousands of Scots into fuel poverty as a result.
The trade union will stage a demonstration outside the Scottish Power headquarters in Glasgow on Friday afternoon.
Unite said more than 150,000 people in Glasgow were already experiencing moderate to severe levels of food poverty due to a "broken economy".
Polling by Survation also found that 28 per cent of Glaswegians have either gone into debt or increased their levels of debt in order to meet the increased cost of grocery items.
Sharon Graham, Unite general secretary, said: "How’s that for trickle-down economics? £7 billion handed over from Scottish Power to Iberdrola in Spain.
"That’s trickle down economics alright. Trickle down from Scotland to Spanish shareholders. Proof that government trickle down policies are doomed to fail. Meanwhile, politicians are abysmally failing workers and their families across Glasgow and beyond.”
She added: "The economy does not work for workers and their families. Britain’s real crisis isn’t rising prices, it’s an epidemic of unfettered profiteering.
"This is why we need to build power in our workplaces and simultaneously organise in our communities. Unite will establish permanent bases on the ground in Glasgow to work with workers. Unite is driving a UK-wide strategy to help bring change to heartland communities."
A spokeswoman for Scottish Power said: "As a business employing thousands in high skilled, high paid green jobs, where our employees – including Unite members – share in our success, we’re disappointed by the union’s action.
"This wilful misrepresentation fails to recognise we invest more in UK energy projects than we make in profit or dividends every single year.
"We’re building the renewable and electricity network infrastructure that will help wean this country off expensive fossil fuels and are creating a record number of jobs to help us do it – even in this difficult economic climate, not to mention having led the call for Government action on the cost of living crisis.
"We stand for £10bn investment in the UK to 2025, delivering on the action needed to tackle climate change and investing in people, with 1,000 new jobs to be created in the next 12 months to help deliver our ambitious investment pipeline. We reiterate to Unite that we welcome constructive engagement.”
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