RAIL bosses are concerned an 11-screen cinema planned for on top of the St Stephen's Green Centre could affect the Dart Underground project.
They have written to Dublin City Council seeking further information on a proposal to place the 1,851-seat development above the shopping mall.
Irish Life Assurance plc, the centre's landlords, and Ventasker Ltd lodged an application with the council for the scheme.
Permission is being sought for the demolition of existing rooftop buildings to make way for the 4,000sqm scheme.
However, the project manager for the Dart plan, Peter Muldoon, pointed out in a letter to the local authority that the structure would be built above the alignment for the subway.
He added the applicant "does not state what mitigation measures ... will be taken to prevent any impact on the tunnelling works".
Mr Muldoon said it is therefore not possible for Iarnrod Eireann to properly assess "if the proposed development poses difficulties for the construction of the Dart Underground".
He requested the local authority seek further details from the applicant on its behalf.
In January, well-known cinema operators the Anderson family revealed it was to invest €9m in the cinema project.
Paul Anderson of the family's Omniplex Holdings said they had signed an "exclusivity agreement" with the landlords.
He admitted it would not be an "easy build".
"Everything will have to be craned into the site," Mr Anderson added.
The project has come up against opposition from property owners in the area.
The project will lead to 100 jobs, it is expected.
If the cinema is built, it will be the first multiplex on the southside of Dublin city centre.