Sanford says it could stop using American Samoa's port after being found guilty of polluting water by dumping oily waste.
The company's vessel, San Nikunau, was accused of failing to comply with the US Federal Act of Pollution from Ships while fishing in waters off American Samoa in 2011.
Sanford Ltd was found guilty of dumping the waste, known as bilge, but not guilty of an obstruction charge in a Federal Court in Washington.
Managing director, Eric Barratt, told Checkpoint the company may look at pulling out of American Samoa altogether.
Sanford says a significant portion of its skipjack tuna catch goes through the Pago Pago port, worth as much as $19 million a year.
A Sanford employee was found guilty of an obstruction charge of falsifying records.
Sanford Ltd faces a fine of up to $US3.7 million following the decision by the court in Washington DC.
Prosecutors say Sanford violated American law by dumping oil waste into US waters in July 2011 without using pollution prevention equipment.
They also said the company covered this up by falsely claiming such equipment had been used.
The United States Attorney's Office for the District of Columbia says the prosecution demonstrates the commitment of the US to enforce environmental laws and protect precious natural resources.
The waste, known as bilge, can be contaminated with oil, lubrication fluids and other liquids that leak from the ship's engines or pipes and hoses.
The company will be sentenced on 16 November.
