The Port Authority says the surprise strike staged by thousands of longshoremen Friday is over.

The workers had walked off the job at Port Authority terminals in New York and New Jersey Friday afternoon, all but shutting down one of the nation's busiest port networks.

The Port Authority said in a tweet that full operations were being restored Friday evening, "thanks to the expedient efforts" of the unions involved. Gates will open as scheduled on Feb. 1.

Members of the International Longshoremen's Association, one of the primary rank-and-file unions at the ports in New York City and New Jersey, stopped working about 10 a.m., according to the Port Authority. The stoppage affected all of the terminals in the port system, which receives nearly 30 percent of all cargo on the East Coast.

A spokesman for the union said the walkout took many union officials by surprise. Another union official told NBC 4 New York the strike was spurred by a bevy of grievances including concerns about the Waterfront Commission of New York Harbor's role in collective bargaining, regulations on time off after injuries and drug testing protocols.

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Several workers told NBC 4 New York they didn't know the strike was happening when they went to work on Friday and they were awaiting instruction on what to do next. The walk-off appeared to be organized and peaceful, however.

In a statement issued after the strike ended, NYSA said the walkout was "extremely disruptive and in violation of the NYSA-ILA Collective Bargaining Agreement."

An emergency contract board meeting held in the afternoon resulted in a deadlock. An arbitrator found the strike was in violation of the workers' contract and ordered the ILA to inform its members, according to NYSA.

During the discussions, the ILA and NYSA agreed to continue talking about outstanding issues like jurisdiction, hiring and technology.

Affected terminals include Port Newark, the Elizabeth-Port Authority Marine Terminal, Port Jersey in Bayonne, Howland Hook Marine Terminal on Staten Island, and the Brooklyn Marine Terminal in Brooklyn's Red Hook neighborhood.

Gridlock was reported near port access points, with hundreds of truckers idling at the gates or inside the terminals. One trucker, Kennedy Twaits, said he was losing a day of work from the stoppage.

"Yeah, A lot of money I lost," he said. "Not only me. Everybody loses money here."

It's not clear how the work stoppage has affected cargo ships.

The Port Authority said in a statement earlier Friday afternoon that police were working to keep people safe, and urged ILA members to "

"As the agency that oversees the largest port complex on the East Coast, we strongly urge the ILA members to return to work immediately and resolve their differences after they return. In the meantime, Port Authority Police are actively working to ensure public safety for all of the stakeholders at the port," the authority said.

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-- Pei-Sze Cheng contributed to this report.