The threat of port labor strikes by longshoremen along the U.S. East and Gulf coasts could cause crippling disruptions to organizations' inventories and supply chains, Marsh Inc. said in a new report released Thursday.

The longshoremen's labor contract with port operators on the East and Gulf coasts is set to expire Dec. 29. Negotiations between the International Longshoremen's Association and the United States Maritime Alliance so far have been volatile, Marsh said in the report, “U.S. Port Strikes — What's At Stake and How To Manage Your Risk.”

A potential strike could disrupt operations at ports from Maine to Texas, including critical ports of New Orleans, New York, New Jersey and Baltimore.

If focused on containerized shipping, which represents one-fifth of all waterborne trade volume in the United States, a potential strike could affect 15 billion cubic feet of cargo with an estimated value of $437 billion, the report noted.

After just after one week of a port closure, organizations that import and export products and foodstuffs could face idle manufacturing plants, rapid inventory depletion, goods in transit backed up at sea and supply chains crippled across the board, the report said.

While many industries could be affected by a strike, retail, agriculture, food, and beverage companies would be hit especially hard because of low inventory levels and tighter supply chains, Marsh said.

“Port closures are painful to supply chains due to the sudden and severe backlog and rerouting pressures they put on organizations and their suppliers,” Marsh said in the report. “For each day of backlog accumulated during a port closure, organizations need eight days to stabilize inventory levels within their supply chain.”

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Companies at risk can diversify port-of-entry locations and consider alternative sourcing and buying strategies, the report said. Companies also can purchase trade disruption insurance, but many insurers often exclude labor strikes as covered disruption unless physical assets are damaged as a result, the report noted.

“Global businesses must be prepared for powerful and possibly crippling disruptions that can happen without warning,” said Gary S. Lynch, global leader of risk intelligence and supply chain resiliency for Marsh Risk Consulting, in a statement accompanying the report.

“Those companies with the right portfolio of risk strategies can more effectively protect themselves from potentially severe losses, while simultaneously gaining market share from less-prepared competitors,” he said in the statement.

The neighboring ports of Los Angeles and Long Beach on Wednesday ended an eight-day strike that reportedly cost the region an estimated $8 billion.

Discussing possible coverage for the Los Angeles dock strike and future strikes, Joe Sheridan, New York-based senior vice president, marine for Lockton Cos. L.L.C., said because a disruption to the supply chain is involved, the most likely coverage would be trade disruption insurance, which would cover profit loss, among other financial losses.

“It's sold by marine markets but is not a traditional marine placement,” Mr. Sheridan said. He said this coverage is generally obtained through Lloyds of London.

However, at least one such policy issued by Lloyd's syndicates would exclude such coverage except where a strike results in physical loss or damage.

The Marsh report is available >a href="http://usa.marsh.com/NewsInsights/MarshRiskManagementResearch/ID/27444/US-Port-Strikes-Whats-at-Stake-and-How-to-Manage-Your-Risks.aspx">here.