The British practice has admitted that there are 'cost challenges' due to the 'soaring cost of property acquisition' and that, as a result, a redesign is being considered.
It is being reported in New York that the scheme - which is on a site neighbouring Ground Zero - is now up to $50 million (£26.6 million) over its $799 million (£425 million) budget.
'To mitigate this, the Metropolitan Transportation Authority and New York City Transit, together with the design team, has been exploring a number of strategies to address project-wide cost overruns,' a Grimshaw spokeswoman said.
'Potential solutions include seeking additional funding, scope modification and limited redesign,' she added.
When the project is finally finished, the new streamlined transport hub will bring together six existing stations and become a key focal point of the regeneration of lower Manhattan.
Handling more than 275,000 passengers a day, the 34,000 sq m interchange will increase the station's capacity to 12 subway lines and will link up with Santiago Calatrava's World Trade Center transportation hub.
The central feature of the current design is a 34m-high asymmetric dome, which will rise above the glazed entrance and pavilion.