It is feared the new National Maternity Hospital will bring south Dublin's traffic to a halt.
Residents in the surrounding area of St Vincent's Hospital say they are not against plans to build the facility on the grounds.
However they say traffic management plans are inadequate.
John O'Malley, Chair of Nutley Residents Association, said: "We're not opposed to the National Maternity Hospital co-locating in St Vincent's, and we haven't objected to that.
"We would submit that the planning application has seriously underestimated the impact the traffic will have, the extra additional traffic will have on the environment," he said.