"I can't tell you the pressure that Project Fear and Remain put on senior business people not to articulate their views," Johnson said on his weekly LBC phone in.
"Everyone has an interest in keeping friendly with government."
Asked by host Nick Ferrari how the government applies the pressure, Johnson replied: "I do not wish in anyway to be disparaging or critical of my friends in government, but it is well-known that there is an operation in Downing Street and you will get a call from certain gentlemen, whose names you can discover - younger, fitter people than us Nick can go out and do the research."
"And they will say 'look, you know, we want to continue to have contracts with you. It’s very important that we want to continue friendly relationships, there is an honours system as you know', all this kind of thing.
"And that’s how it is. There is a bit of leaning on."
Johnson went on to cite a letter from 350 business people stating they want to Leave the EU.
The former London mayor added that he would support David Cameron remaining as Prime Minister even if there is a vote to Leave the EU.
James McGrory, chief campaign spokesman for Britain Stronger In Europe, said: "These are desperate claims from Boris Johnson, who knows his campaign is badly losing the economic argument.
"The reason the overwhelming majority of businesses back staying in the EU is because it makes economic sense.
"Voting remain will secure more jobs, lower prices, and a decent, tolerant United Kingdom."