Rachel Reeves has been warned not to "balance the books on the backs of retail workers" through an overhaul of business rates.
In a rare joint appeal, shop workers union Usdaw and the British Retail Consortium said the Chancellor must "protect shops and those who work in them" in the Budget in November.
Nearly 3 million people work in retail in Britain but pressures on the sector have seen 350,000 jobs lost over the last decade. More than 10,000 shops closed last year.
Labour has promised to reform business rates to get high streets thriving with plans for a permanent cut for retail, hospitality and leisure properties from next year.
To fund the changes, the Treasury is considering increasing business rates for any large non-domestic premises, such as office blocks and banks. But there are fears that larger shops could be impacted.
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Writing for the Mirror, Joanne Thomas, General Secretary of Usdaw and Helen Dickinson, Chief Executive of the British Retail Consortium, said: "It could hit the very supermarkets and anchor stores that employ a third of the people in retail and attract customers onto our high streets.
"For those larger shops it could mean fewer hours for employees, and the risk of more shuttered shops and job losses. We also know what it would mean for prices.
"Retailers work hard to hold down costs for as long as possible, but when costs keep rising, prices are pushed up.
"Working people - union members, Daily Mirror readers - end up paying more at the till. Nobody wins."
They are urging the Government to exclude shops from a new higher business rates band - and instead hike the rates paid by large office blocks and other big commercial buildings.
They said: "We’ve all seen the gap left by the empty department store and how it leaves a scar on the high street. Even when stores can avoid closing, it can mean fewer hours for employees, fewer opportunities for training, and slower pay progression.
"When a larger store cuts back, the café next door, the barber and the chemist all feel it - because when investment is lost, so too is the footfall.
"Let’s put fairness at the heart of the Autumn Budget, back good jobs and raise living standards. Let’s not balance the books on the backs of retail workers."
A Treasury spokesperson said: “We are creating a fairer business rates system to protect the high street, support investment, and level the playing field by introducing permanently lower tax rates for retail, hospitality, and leisure properties from April that will be sustainably funded by a new, higher rate on less than 1% of the most valuable business properties.
“Unlike the current relief for these properties, there will be no cash cap on the new lower tax rates, and we have set out our long-term plans to address ‘cliff edges’ in the system to support small businesses to expand.”
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