"Alstom lodged a complaint on Tuesday at the High Court in London to demand that the call for tender by Eurostar be suspended," the spokeswoman said.
Alstom, the pride of French engineering and currently the only company making trains to run in the Channel tunnel, says the high-speed trains made by Siemens do not meet safety regulations for the route.
The French company faces increasing competition as railways in the European Union are open up to competition under EU rules.
"This call for tender cannot be concluded since the train specifications set by Eurostar do not correspond to the regulations demanded for a train going in the Channel Tunnel," the spokeswoman said.
Eurostar, the cross-Channel rail monopoly jointly owned by France, Britain and Belgium, has ordered 10 of Siemens's new-generation high-speed Velaro trains.
France's transport minister Dominique Bussereau said last week: "Equipment other than that currently made by Alstom cannot go in the tunnel, so Eurostar's decision is null and void."
Alstom complains that Eurostar's call for tender anticipated a future change in safety regulations which allowed Siemens to bid.
Siemens replied Wednesday to the legal challenge by saying it was confident of retaining the deal.
"Competent courts will rule if the procedure and attribution of the contract to Siemens was fair," a statement said. "We are confident that is the case."
"The complaint was not directed against Siemens," it added. "Siemens made an offer as part of a transparent process that conforms to European law, and which was deemed best by the client."
Both Siemens and the German railway Deutsche Bahn are counting on deal to advance cross-border rail competition in Europe.