A new risk to global supply chains is emerging as exhausted seafarers stuck offshore for months halt work, a breaking point caused by restrictions on crew changes amid coronavirus precautions.

Three vessels are idled in Australia after crews who worked beyond their contracts demanded to be repatriated, according to the International Transport Workers’ Federation. The organization’s national coordinator in Australia, Dean Summers, said he is discussing options for about four other ships, without elaborating.

As of Friday, the Conti Stockholm, Ben Rinnes and Unison Jasper vessels are idle at the ports of Fremantle, Geelong and Newcastle, respectively, the union said in a statement. The three ships are “just the tip of the iceberg,” Summers said in the statement, adding that crews are within their rights to refuse to sail.

“The COVID-19 pandemic has made crew changes extremely difficult, and we’re starting to see fleet inefficiencies emerge,” Braemar ACM Shipbroking Ltd. said in a report dated Aug. 6. “A huge number of seafarers on merchant ships have been unable to disembark once their contracts have ended, facing excessive times at sea and away from home.”

In addition to Pacific routes becoming less efficient for bulk carriers, there’s been a pickup in shipowners opting for lengthier deviations to places such as Kochi in southern India, Braemar said, referring to merchant ships that transport cargo such as grains, coal and iron ore. Atlantic supply doesn’t seem to have been impacted too heavily, it added.

According to the International Chamber of Shipping, about 250,000 seafarers are stuck at sea at increasing risk of physical and mental exhaustion. This could have an impact on safety as fatigue raises the risk of human error and accidents, said Ralph Leszczynski, head of research at shipbroker Banchero Costa & Co.

“Individual members of crews might have important personal reasons to want to be repatriated as soon as possible, but currently the costs and logistical challenges to send them home are enormous,” Leszczynski said.

Of the three vessels idled in Australia, the Unison Jasper was hauling alumina and the Ben Rinnes was chartered by Cargill Inc. to transport soy, the ITF. said. The Conti Stockholm is a container vessel.

“We are frustrated to learn of crew members being over contract on the Ben Rinnes, which is unfortunately one of many such cases at the moment,” a spokesperson for Cargill said, adding that the firm recognizes the challenges that many crew are facing and is working to try and repatriate them.

Many on the Ben Rinnes have been aboard for longer than the legal maximum, including one crew member who has been on the ship for more than 17 months, ITF said. The crew signed five-month extensions on top of their nine-month tour after the vessel owner promised to repatriate them, the union said.

The Conti Stockholm is in Fremantle while a solution is being is worked out, a spokesman from the port said. The Port of Geelong confirmed the Ben Rinnes is docked at a berth and said the crew is in “discussions with the relevant agencies including the shipping agent and the Australian Maritime Safety Authority around crew changes.”

The Unison Jasper is in the port of Newcastle, however its status is a matter for the AMSA, a spokesperson for the port said.