More than 70 of the UK's biggest retailers, including giants such as Tesco, Asda and Next have written to the chancellor to warn her national insurance hike will result in shop closures, job losses and price increases.
The joint letter insists the "sheer scale" of the costs incurred by businesses because of the move would make job cuts "inevitable".
Signatories of the letter, including Amazon, Boots, Greggs and JD Sports, the accumulation of changes such as the employers' national insurance contributions rise, increasing minimum wage and new levies on packaging could send industry costs rocketing by up to £7billion.
The letter was organised by the British Retail Consortium - in spite of attempts by the Treasury to dissuade it from doing so.
In it, the dozens of retailers warn: "For any retailer, large or small, it will not be possible to absorb such significant cost increases over such a short timescale.
“The effect will be to increase inflation, slow pay growth, cause shop closures and reduce jobs, especially at the entry level.
“This will impact high streets and customers right across the country."
Rachel Reeves is standing firm on her Budget despite taking fire on several fronts - not least from furious farmers set to flock to Westminster in their thousands today to protest changes to inheritance tax.
A spokesman for the Treasury told The Times: “With our public services crumbling and an inherited £22billion fiscal black hole from the previous government, we had to make difficult choices to fix the foundations of the country and restore desperately needed economic stability to allow businesses to thrive.
“By doing this, more than half of employers will either see a cut or no change in their national insurance bills, there will be £22.6billion more for the NHS and workers’ payslips will be protected from higher tax. This government is committed to delivering economic growth by boosting investment and rebuilding Britain.”