The company claims that the extension of berthing facilities on the northside of the port is necessary to cater for future demand.
However, there are over 200 objections mainly from local groups in the Clontarf area who say the expansion could cause flooding.
The hearing, which is expected to last a number of weeks, is also to hear arguments about economic justification for the expansion.
The Department of the Environment is also due to extend the special protection area for wildlife in Dublin Bay and it is understood part of this would include the proposed port extension.
