Service tax applicable rate change on 40% on composite schem

Sir,

We have issued a work order to the contractor,as per corrent rule service tax shall applicable on 40% of Basic value as this is the service portion and 60% is the material portion ( On composit scheme)

Now the material portion rate has incresed(Cement ,steel, Etc) and order has revised with incresed rate of material portion.

Now contractor raised the addisitional bill for material rate change, 

Can the contractor claim the service tax on this incresed rate of material value ?

Plz send the valuable comment.

B.Regards

Amaresh Mohanty