Unionists are accusing Ports of Auckland of trying to wreck workers' family Christmas celebrations with "intimidating" letters threatening to contract out their work.
The company denied trying to browbeat its staff, 327 of whom held their third strike at the weekend and were earlier locked out for two days, saying it simply wanted to be truthful in outlining potential work practices.
But the Maritime Union said the company's management had wrecked any chances of an early settlement of a dispute that has already disrupted the handling of 10 ships at an estimated cost to the Auckland Council-owned port of about $2 million.
"These families, right on Christmas, are getting these things saying their husbands and fathers will be redundant - it's an attack on the families," said union branch and national president Garry Parsloe.
Company chief executive Tony Gibson confirmed an offer to not contract out any more work or make staff redundant during the term of any new collective employment agreement had been withdrawn.