The amount of cargo that moved through the Port of Long Beach in January took a nearly 19 percent nosedive compared to the same month last year because of ongoing congestion and labor strife, officials said late Wednesday.

Nearly 429,500 containers moved through the port last month, an 18.8 percent drop from January 2014. Imports fell 23.5 percent while exports fell 19.6 percent. By comparison, 528,900 containers moved through the port last January and 536,300 containers moved through two years ago.

This was the Long Beach port’s slowest month since February 2012, when just 388,600 containers moved through the docks.

Port officials blamed the slow month on the months-long contract negotiations between shipping lines and the dockworkers’ union, which have sparked work slowdowns and cuts in work shifts, as well as other congestion issues. Until the Pacific Maritime Association, which represents shipping lines, and the International Longshore and Warehouse Union, agree to a new contract, officials said the backlog of containers on the docks waiting to be loaded or unloaded won’t be cleared and container ships off the coast will continue to wait for space at port piers.

“We are encouraged by recent progress through federal mediation and are hopeful that the contract will be signed soon, so that the port complex can focus on returning operations to a normal pace,” said Port of Long Beach Chief Executive Jon Slangerup.

The Port of Los Angeles, which usually reports cargo container volumes at about the same time, will not report numbers until next week, a spokesman said, because congestion has delayed reports from the cargo terminals.