The CEO of Lyttleton Port says double-digit pay demands are what's holding up a deal with its workers.

A 24-hour strike notice has been issued for next month after talks to improve safety and pay failed.

Rail and Maritime union organiser John Kerr says the company has no fatigue management policy, as it moves towards a 24/7 port operation.

CEO of the Port Peter Davie says workers are demanding wage increases of between four and 15 percent which the company cannot meet.

He says it's offering annual salary increases of at least three percent for the next three years.

Peter Davie says they've been in talks over fatigue management with the union for some time, and it's disingenuous for the union to now criticise the process.