Talks between the union representing nearly 15,000 dockworkers from Maine to Texas and the alliance representing shipping companies and port operators, stalled last week as both sides traded accusations. The union represents about 1,400 Baltimore longshoremen.
Management says the royalties amount to additional compensation and wants to cap payments at 2011 levels.
Union leadership says it will not negotiate any changes to the formula.
George Cohen, director of the Federal Mediation and Conciliation Service, said no additional information would be made available "due to the sensitive nature of the negotiations."
A strike would shut down all containerized cargo in Baltimore, but would not affect bulk cargo, automobiles or cruise ship traffic.