The Maritime Union heads back into mediation talks with Ports of Auckland management today.

The union's issued a second strike notice following four months of negotiations around its collective agreement.

The port company responded by issuing a lockout notice for two days in retaliation.

Union president Garry Parsloe says the strike action so close to Christmas shows the determination of the workers.

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"They will suffer financially right on Christmas, it will damage their wages and what they can take home to their families, but at the end of the day they're that serious and that determined to get some sort of integrity and credibility around this load of negotiations."

Parsloe says the port will still be working during the industrial action.