The outspoken Foreign Secretary hit out at Carolyn Fairbairn, head of the CBI, for saying Britain must remain in the customs union.
Mrs Fairbairn claimed keeping close ties with the EU would be “best for jobs, wages and living standards” after we quit the bloc.
But Mr Johnson said such a move would mean “effectively staying in the EU” because the UK would be forced to obey Brussels’ rules.
He tweeted: “Makes no sense for the CBI to keep calling to stay in customs union. PM was clear in Florence speech we are leaving.
“Brexit means taking control of laws, borders, money, and trade. I’m confident British business can profit from the new opportunities.”
“Staying in the customs union means effectively staying in the EU: the EU *is* a customs union.
“It means no new free trade deals, no new export opportunities, and no leading role in the World Trade Organisation.”
And Richard Tice, co-chairman of pro-Brexit group Leave Means Leave, accused the CBI of being “back in Project Fear mode”.
He told the Sunday Express: “It is astonishing that the secretive CBI – which refuses to state its fee-paying membership yet claims to be the voice of business – appears to know little, if anything, about the business world.
“Calling for negotiators to ‘revisit red lines’ will guarantee a bad deal for the UK. It will weaken our hand and is the worst strategy the Government could adopt.
“As anyone in business knows, no deal is better than a bad deal and the Government has accepted that.
“Only by leaving the customs union can the UK forge new independent trade deals with the rest of the world.”
The Department for Exiting the EU said it was “confident of negotiating a deep and special economic partnership that includes a good deal for financial services”.
A spokesman added: “We have already made good progress, having reached an agreement with the EU on a range of issues such as citizens’ rights and the financial settlement.
“But, as the Prime Minister has already made clear, we will be leaving the single market and the customs union after EU exit day.”
It comes as Tory MPs prepare to demand that Mrs May ends free movement the moment the UK formally quits on March 29 next year.
Jacob Rees-Mogg, chair of the influential European Research Group, said it would be “absurd” to continue with the arrangements after Brexit.
He said: “We must have control of free movement of people as soon as we leave.
“This idea that we can let them carry on coming for another two years is absolutely absurd.”