49 CFR 1333.2: Who may charge demurrage and who may enter into contracts pertaining to demurrage.

A serving carrier and its customers (including those to which it delivers rail cars at origin or destination) may enter into contracts pertaining to demurrage. Additionally, a third-party intermediary may enter into contracts with a shipper (or consignee) that the shipper (or consignee) shall be billed for demurrage pursuant to section 1333.3(b). However, in the absence of such contracts, demurrage will be governed by the demurrage tariff of the serving carrier.