Speaking to the BBC's World at One programme, Mayfield said John Lewis wasn't "taking sides" – before going on to state a UK departure from the EU could lead to job losses. A weaker currency could also mean prices rise.
"You have to have respect for the fact that people have very different views, but as a businessman, looking at the economic issues, I do think that the economy will be stronger if we remain in the European Union," he said.
"That does matter, it matters to jobs, wages and public services because they do depend on how the economy's performing."
On being asked whether he saw a long-term economic benefit to leaving, in spite of an immediate negative impact, he said the business had examined the risks and found it "harder to see the upsides".
Mayfield's comments come as multiple polls give the Leave campaign the lead, and The Sun newspaper declaring itself in favour of Brexit.
Sir Terry Leahy, former boss of Tesco, warned this week that Brexit was a "leap into the unknown" and also warned that food prices might rise. Leahy, ex-Sainsbury's boss Justin King, ex-M&S boss Marc Bolland and ex-Kingerfisher chief executive Sir Ian Cheshire penned a joint article in May warning against Brexit.