Services provided to entity(negative list) taxable??

Hello Everyone

An entity, say M, is providing services covered under 'negative list' but for carrying business it deal with other entities say A,B,C etc which are providing 'Taxable Services' to M

Can any one tell me, whether A,B,C etc can charge Service tax on services provided by them to M.

And if not, under which provision/rule/notification/circular which specify that they can't charge service tax from M?

Thanks