P&O Ferries has accused port authorities in Liverpool of unfairly stopping supplies reaching Dublin after a row over payment.
The firm said the departure of the Norbay - carrying food and medicine for retailers, including some in Northern Ireland - was prevented after The Mersey Docks and Harbour Company demanded payment of £600,000.
While P&O said there was a payment due, it was less than £0.6m and that it had been in talks with someone at the port who turned out to be furloughed.
A spokesman for P&O said: "We had asked for flexibility in the time required to pay but the Liverpool port refused to respond, even though we were committing to full payment. Then we learned that our point of contact had been furloughed and they didn't tell us.
"The irresponsible and unnecessary actions of The Mersey Docks and Harbour Company at a time of national crisis have closed an essential Liverpool-Dublin supply route, which means vital goods will not be able to flow between the UK, Ireland and Europe."
But a spokeswoman for Peel Ports, which owns the docks at Liverpool, said: "Any decision to detain a vessel is always taken as a last resort and only when there is a significant debt to repay.
"While we understand that we are in unprecedented times, the government has announced multiple financial interventions to support companies with short-term funding issues as a result of Covid-19. These should be used as opposed to passing the cash-flow risk along the supply chain.
"Other ferry services from Liverpool to both Dublin and Belfast continue to operate, with multiple departures per day and spare capacity."
Aodhan Connolly, director of the NI Retail Consortium, said: "Getting goods from Great Britain to the island of Ireland is integral to the food supply chain and for food processing.
"Anything that disrupts this cannot be welcomed at the best of times but now, at a time when we need to keep all supply chains running smoothly, it is particularly unwelcome.
"It is critical this is resolved quickly and is a one-off occurrence."