Some 2,300 security guards organised by the Norwegian Union of General Workers (NAF) are on strike nationwide over pay, and an additional 85 will go on strike from Saturday unless the dispute is resolved first.
A gradual shutdown would have to start on Friday to prepare for the strike the following day, Gassco's systems operations chief Alfred Hansen said.
"In order to shut down a facility like Nyhamna and to do it in a safe and proper manner, we would have to start a while before," Hansen said. "So we warned our shippers in the transportation system that this potential is now clear and that we are preparing for this scenario tomorrow."
The Norwegian government, which can invoke emergency powers to end workplace conflicts, said it was closely monitoring the situation but declined to say whether it would step in.
Nyhamna processes gas from the Ormen Lange and Aasta Hansteen fields, which would also have to shut because of the strike, Gassco and the Norwegian Oil and Gas Association (NOG) said.
Export capacity from Nyhamna stands at 84 million standard cubic metres (mcm) of gas per day, about a quarter of Norway's expected 330 mcm export volume on Thursday.
The NAF union confirmed that security guards working at Nyhamna were among those who would join the strike, but declined to give numbers.
Security guards are also on strike at heliports from which crews and equipment are flown to and from offshore platforms, and the gradual escalation of the conflict could disrupt supply lines, oil major Equinor said.
While governments can end strikes, they are generally reluctant to do so. In 2012, the government ended a strike after 16 days when employers threatened a lockout of workers that would have shut down all oil and gas output.
"The ongoing dispute is for the parties to solve, but the ministry is following the situation closely," a spokeswoman for the labour ministry said.
(Writing by Terje Solsvik; editing by Alexandra Hudson and Barbara Lewis)
By Nerijus Adomaitis and Nora Buli