Union officials representing more than 120 engineers and deck staff on the Interislander ferries say striking is "always an option" if an agreement can not be reached with KiwiRail by the end of the week.
The parties have been in talks over work conditions for seven months.
Merchant Service Guild general secretary Helen McAra said no passenger services had been affected by the negotiations, but a strike was "always an option".
"There has been talks of strikes but it's our hope that it doesn't come to that."
The guild represents 54 deck officers who could vote on an offer from KiwiRail by the end of the week.
The Aviation and Marine Engineers' Association is representing 70 engineers, and an official said it hoped to have a redrafted agreement from KiwiRail by today. The engineers could then decide whether to vote on the offer.
The bargaining, which began in March, involves the pay and work conditions covered under the workers' collective employment agreements.
A KiwiRail spokesman declined to comment on specific points of negotiation. Negotiations for collective agreements took "some time" to work through, he said. "We are working constructively with all the parties involved in this process and [are] happy with how negotiations are proceeding."
McAra said the union had not filed any notice of strike action and was required by law to give KiwiRail 14 days' notice.
The guild represented all deck officers working on the Interislander ferry service and it would take about a fortnight for the results of their ballots to be concluded, she said.
"They don't want to lose any conditions that they have now. We're in the final stages of meeting a settlement . . . [and] both parties are using their best endeavours to come to an agreement."
The agreement covered areas such as superannuation, holiday leave and hours worked. There were no disputes about "physical issues" such as onsite health and safety.
Bargaining had been a slow process but the company was "motivated" to hear what the workers wanted, she said. The last collective agreement renewal was in 2010.
Aviation and Marine Engineers Association national industrial organiser Stan Renwick said the engineers would meet today to discuss an offer and decide whether they wanted to put it to a ballot.
Striking was an option if union members rejected the offer, he said.
- The Marlborough Express