Maritime Unions like ITF (International Transport Workers’ Federation) can blacklist a ship if ITF disagree with the terms of the crew’s contract of employment.
ITF (International Transport Workers’ Federation) is known to concentrate its efforts in certain areas such as Scandinavia and Australasia, where shore labor such as stevedores or tug crews may support seafarers in disputes and prevent ships from entering ports or from sailing.
In time charters, shipowner does not want to find his ship blacklisted by ITF (International Transport Workers’ Federation) at the time or later.
Therefore, the shipowner will seek to exclude such ports from those to which the ship may be traded by the disponent shipowner (time charterer).
In same manner, voyage charter-party forms are incorporated clauses relating to strikes and lock-outs as well as politically motivated blockades and other warlike actions.