Major tonnage provider Seaspan Corp is keeping a close eye on US plans to impose extra punitive port fees on Chinese-built ships.

Parent Atlas Corp said in a filing that the proposed action to slap a levy of up to $1.5m on each terminal call is subject to a period of public comment and hearings before it is implemented.

“It is unclear … how the proposed service fees will be levied and which party involved in the operation of a Chinese-built vessel will be required to pay the fees,” the company added.