Leaving the European Union would threaten jobs, hit investment and make it more difficult to recruit skilled workers from overseas, a new report has warned.
Recruitment firm Manpower said a No vote in the referendum promised by Prime Minister David Cameron could have a negative effect on the economy as firms struggle with a "serious" shortage of skilled staff.
So-called Brexit would create a "vast amount" of uncertainty and instability in the UK economy, Manpower said after surveying 2,100 employers.
The study found that firms were facing a "critical" shortage of skilled workers, especially in the North of England.
Official figures showed that employment in the UK is at a 40-year high, but many employers are struggling to fill vacancies, said Manpower.
James Hick, of Manpower, said: "While many employers in the South can rely on a steady supply of workers, there are far fewer qualified candidates in the North.
"With a shortage of skilled trades, IT and engineering skills, employers looking to increase hiring in the coming quarter, skills shortages threaten to hamper business growth plans.
"George Osborne may dream of a Northern Powerhouse, but the reality will be a Northern power cut if we don't see more talent coming into the market."
Mr Hick said it was difficult to see where the thousands of promised new GPs will come from because there were not enough home-grown clinicians.
He added that the EU referendum was a good opportunity to debate the impact of free movement and immigration on UK jobs.
"Our position is clear - leaving the EU would threaten jobs and harm Britain's prospects.
"Brexit would create a vast amount of uncertainty and instability in the UK economy, making companies less willing to invest in new jobs.
"It would also reduce the flexibility of the UK workforce, with companies less able to attract talent from abroad."