Dublin Chamber of Commerce has hit out at a new traffic plan for the city centre, which bans motorists from turning right at Bachelors Walk.
It said the plan would have a "devastating effect" on businesses.
Starting yesterday, private motorists were barred from taking a right-hand turn across O'Connell Bridge from the quay.
General traffic has also been reduced to one lane from Upper Ormond Quay to Eden Quay on the northside, and from the Rosie Hackett Bridge to Wellington Quay on the southside.
A member of An Garda Síochána managed traffic at the junction on Monday morning, informing drivers of the changes.
"It's like turning off a light switch, hoping everyone will find their way around in the dark," Graeme McQueen, of Dublin Chamber of Commerce, said.
"We won't be able to get a full idea of the impact this new incentive will bring until mid-September when the schools are back. Dublin City Council is hoping this change will work, but we've yet to see any real evidence about how it will pan out.
"There's been no concrete plan around it at all, which is why the business community is so nervous."
Adrian Cummins, CEO of the Restaurants Association, said delivery drivers would now take twice as long getting into the city centre.
"The whole drop-off routine for deliveries is going to be a major problem due to this change.
"Businesses are outraged with the arrogance of Dublin City Council, who are rolling out these new projects without consulting them.
"This is a total anti-business project in my opinion."
Mr Cummins added that he believed the council acted like a dictatorship. "It's always their way, or no way at all. So many business owners have contacted me about how they're not being listened to.
"Dublin City Council is being run like a dictatorship in my opinion because they don't listen to anyone, not even elected councillors," he said.
But the city council said the changes were being introduced to reduce delays experienced by public transport users, and to ensure that Luas Cross City is subject to minimal delays.
Head of technical services Brendan O'Brien said the changes would help minimise delays and allow freer movement of public transport across the city as the number of commuters rises.
"Additional bus lanes will alleviate the difficulties faced by public transport on the quays, where the worst delays for buses in the city are experienced," he said.
"At the peak morning time of 8am to 9am, over 7,000 people travel along the north quays on buses.
"This compares to around 500 cars and the same number of cyclists."