MP Theresa May has expressed concern about the new Crossrail in a meeting with the chairman of the project.
Her main worry was that the service would result in a reduction in fast trains from Maidenhead to London Paddington.
Crossrail, which will operate as a stopping service, is expected to be finished in 2019.
The Home Secretary said: "Crossrail has the potential to bring significant benefits to Maidenhead, but we must ensure that it is not seen as an excuse to reduce the existing fast services that people rely on.
"I am disappointed that there will be no fast services available via Crossrail.
"Maidenhead residents and businesses will continue to need fast, non-stopping services and Crossrail must complement these, not replace them."
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