John Kerr, the union's South Island organiser, said the members had voted to strike again before Easter, but held off issuing a notice in hopes the two parties could come to a proper resolution.
"There have been discussions, but once again LPC has rejected any compromise we suggested," Kerr said. "They remain determined to force our members to pick between inferior pay and conditions, or unsafe rosters."
However, the port says the union rejected three separate options it suggested, and the union's offer is too expensive for it to accept.
"The sticking point is that the RMTU want the same 4 per cent salary increase in the first year that their workmates in MUNZ received, but they refuse to make the roster changes MUNZ members already have made," said chief executive Peter Davie.
"RMTU claim the roster changes agreed to by MUNZ are unsafe. It is ludicrous to think we would ever put forward unsafe changes and the 201 MUNZ members have no safety issues with the roster changes."
Lyttelton Port manages more than half of the South Island's containers and 70 per cent of imports, the port said. In their press releases, both sides stressed the importance of the port to the South Island's supply chain.