Lyttelton Port's failed legal action against its workers has riled the Rail and Maritime Union.

The Employment Court rejected the company's injunction against workers who refused to cover weekend shifts on health and safety grounds - saying it's unlawful.

The Rail and Maritime Union says its ban on overtime will remain until they reach an agreement.

Organiser John Kerr says he's glad the court saw sense.

"The port company were alleging this was a ploy by our union in relation to the breakdown in negotiations and pay talks. Clearly that wasn't the case and the judge has agreed with us."