The contractor is asking for a material that costs 4 times more than the other two materials that are suitable for the project. They have a spec that calls out for a geo fabric material but only one geo material will comply as the manufacturer holds the patent and no other manufacture can make at this time. There are two other manufactures that can provide a material with similar qualities.
That's a pretty fact-specific situation believe it or not. The answer will depend on a few things. You'll want to talk to an experienced construction attorney and walk them through the situation. They'll ask, what does your contract say? Does it allow for "or equals" and what is the submission process for that--and did you follow it? Was the specification in the plans/specs that you bid?