Detention and demurrage invoices arrive with an air of finality — a number, a container, a due date. Since the Ocean Shipping Reform Act of 2022 and the Federal Maritime Commission rulemaking that followed, that finality is less real than it looks. The rules impose specific requirements on what a demurrage or detention invoice must contain and how quickly it must be issued, and an invoice that misses those requirements is on shaky ground.
This is not a promise that you can make charges disappear. Plenty of demurrage is legitimately owed. But a meaningful share of invoices are defective, late, or unsupported, and importers who check tend to recover money that importers who don’t never see.
First, the vocabulary
Demurrage accrues when a loaded import container sits at the marine terminal past its free time. Detention accrues when you keep the carrier’s equipment outside the terminal too long — most commonly an empty you haven’t returned. Per diem is the equipment rental variant of the same idea. If those distinctions are fuzzy, our breakdown of demurrage, detention and per diem covers them properly.
What the FMC billing rules require
The core of the framework has three parts.
1. Required invoice contents
A demurrage or detention invoice must carry a defined set of information so the billed party can actually evaluate it. That includes identifying details (container number, bill of lading number, port of discharge), timing details (the date the container was made available, the date free time began and ended, the specific dates charges were assessed), rate details (the applicable rate and how the total was calculated), and dispute details (a clear statement of how to request mitigation, refund or waiver, and where to send it). Invoices also carry certification language attesting that the charges comply with applicable regulations.
The consequence built into the rule is the important part: if the invoice omits required information, the obligation to pay the charge is eliminated. That is a strong lever, and it’s the first thing to check.
2. A 30-day issuance deadline
The billing party generally must issue the invoice within 30 calendar days from the date the charge was last incurred. Invoices that surface months later — and they do — fall outside that window.
3. A 30-day dispute window and a resolution clock
The billed party gets at least 30 calendar days from invoice issuance to request mitigation, refund or waiver, and the billing party is expected to attempt to resolve the request within 30 days of receiving it. Miss your window and you lose the procedural argument even if the substantive one was good.
A note on who can be billed
The rule originally restricted which parties a carrier could invoice. A D.C. Circuit decision in World Shipping Council v. FMC vacated that provision, and the FMC subsequently removed it. As of 2026 there is no bright-line federal rule dictating exactly who may be invoiced, so the question of whether you are the right billed party is governed by your contracts rather than by that regulation. The invoice-content and timing requirements were not disturbed. Because this area has moved recently, confirm the current state of the rule with counsel before relying on it in a significant dispute.
A practical dispute checklist
- Diary the deadline the day the invoice lands. Everything else depends on filing inside the window.
- Check the invoice against the required contents. Missing free-time end date? Missing rate calculation? Missing dispute instructions? Note each omission specifically.
- Check the issuance date against the last day charges accrued. More than 30 days is a problem for the biller.
- Reconstruct the timeline from your own records. Vessel discharge, customs release, terminal availability, appointment attempts, out-gate. Your drayage carrier should be able to produce appointment records and gate timestamps.
- Look for days the container was not actually retrievable. Terminal closures, equipment unavailability, appointment systems with no slots, a container buried and not accessible, a hold that hadn’t cleared. Charges that accrue while pickup was impossible are the classic mitigation argument.
- Write the dispute as a document, not an email complaint. Container number, invoice number, amount disputed, each ground stated separately, evidence attached, and the specific relief requested.
- Escalate if it stalls. The FMC operates a Consumer Affairs and Dispute Resolution Services office that handles informal complaints, and formal proceedings exist for larger matters.
The arguments that tend to work
Container was not available. If the terminal listed the box as available but no appointment slots existed for those days, you have a documented case that the free time was illusory. Screenshots of the appointment system with timestamps are worth more than a narrative.
Hold or exam prevented pickup. Days lost to a customs exam are frequently mitigated, particularly where the exam was not attributable to anything the importer controlled. Our guide to customs exams in Miami covers how those timelines typically run.
Empty return was refused. Detention and per diem charges that accrue because a depot turned your driver away, or because no return location would accept that equipment type, are among the most winnable. Document the refusal at the time — the driver’s photo of the depot notice is the evidence.
Defective invoice. Cleanest of all, and the one importers overlook most.
Prevention beats disputes
Disputes cost administrative time even when you win. The structural fixes are unglamorous: get customs clearance filed early enough that the container is releasable the day it’s available, know your last free day and work backward from it, use a pre-pull when the terminal clock is about to run out and your dock isn’t ready, and have somewhere to put the box that isn’t the terminal. An off-dock yard converts an expensive terminal clock into a cheaper, more predictable storage cost, which is usually the single biggest lever on this line item.
Empty returns deserve their own attention, since detention keeps running until the box is back. Our post on stopping per diem on empty returns goes through that side.
Frequently asked questions
Can I refuse to pay a demurrage invoice that’s missing information?
The FMC rule provides that failure to include required information on a demurrage or detention invoice eliminates the obligation to pay that charge. In practice you should dispute in writing within the stated window, cite the specific missing elements, and keep the correspondence rather than simply not paying.
How long do I have to dispute a detention or demurrage charge?
The rule provides the billed party at least 30 calendar days from invoice issuance to request mitigation, refund or waiver, and the billing party is expected to attempt resolution within 30 days of receiving that request. Your contract may allow more time, but never less than the regulatory floor.
Does a customs exam stop demurrage from accruing?
Not automatically. Charges generally continue to accrue during an exam, but the days a container was genuinely unavailable because of a government hold are a common and often successful basis for requesting mitigation. Document the hold placement and release dates.