Bosses lack information about how self-isolation and testing will work in future, the British Chambers of Commerce (BCC) said.
The group warned an uneven approach to safety could undermine public trust in re-opening.
Mr Johnson announced on Monday that the government planned to scrap England’s social distancing rules on 19 July even though infections are surging, driven by the Delta variant, and much of the population has not been fully vaccinated.
The prime minister admitted he may have to reimpose lockdown restrictions in winter.
Sajid Javid, the new health secretary, said on Tuesday morning that cases could hit 100,000 per day following the end of lockdown.
The BCC’s director-general, Shevaun Haviland, said in a statement: “Businesses in England still do not have the full picture they desperately need to plan for unlocking. Firms do not yet know the future of self-isolation rules, if testing will remain free for them, or when international travel will open up effectively.
“Without clear guidance for businesses around the new proposals, there could be real uncertainty on how they should operate going forward and what they should be doing to keep staff and their customers safe.
“This could lead to a fractured, patchwork approach with very different positions being taken by many businesses, across many locations. That, in turn, could severely undermine the public’s trust in reopening.”
The Confederation of British Industry welcomed Mr Johnson’s plan to fully reopen the English economy but said ministers must now provide more details to build confidence in consumers and owners.
Its leader, Tony Danker, said: “Knowing whether workplace testing will continue beyond July, gaining clarity on mask wearing for public transport and understanding how a test-and-release scheme can support both domestic industry and our international travel sector can provide a further boost for firms.”
The Federation of Small Businesses (FSB) said the government had “a huge amount of work” ahead to convince bosses it was on the right path, warning that “previous false dawns have proved disruptive and disappointing”.
FSB chair Mike Cherry had a string of questions for ministers before the announcement, which the group said were still unanswered after it.
In a statement, he asked: “Is this intervention confirmation enough to buy stock and get staff in place for 19 July? What do I say to staff worried about the safety of public transport? Where do I stand if I lift all restrictions at my business and someone contracts covid on site? Do I tell staff the office is safe to reopen?
“How will the rules around schooling and childcare change? What police protection will there be for me if I ask customers to follow safety procedures and they refuse? What infrastructure, like testing, will be kept in place for businesses?
“After enforcing restrictions for so long, the government must not simply withdraw and allow a free-for-all. A key concern for employers especially will be liability as rules are replaced with guidance. Risk must not be passed on to small business owners.”
Unions are also worried about how the end of restrictions will be managed.
The TUC said it was unacceptable for government to “outsource its health and safety responsibilities” by withdrawing the requirement to work from home where possible and placing on employers the onus for ensuring a safe return to work.
The Independent has contacted the health and business departments for comment.
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