The general secretary of the Fiji Trades Union Congress, Felix Anthony, was arrested by police at his Lautoka home last night.
The Director of Public Prosecutions said Mr Anthony is to be charged with breaching the Public Order Act.
Mr Anthony is alleged to have made false statements to a reporter in relation to the expiry of employment contracts for workers at the Water Authority of Fiji, "which tended to create or foster public anxiety".
He is expected to appear in court at 2pm local time.
Mr Anthony was also arrested on 1 May just as union leaders were planning a mass protest.
On that occasion Mr Anthony was held in custody for two days along with other union members and workers from the Water Authority.
Earlier this week, Mr Anthony told RNZ Pacific the congress would not rest until the government honoured an agreement with the country's workers.
The government had agreed to law reform and issues essential to national industries as well as to provide unions with an equal seat at the table, Mr Anthony said.
Last week, he attended a meeting in Geneva where he said the International Labour Organisation (ILO) had put the Fiji government on notice over its failure to implement reforms agreed to in 2016.
It has been given until November this year to show progress, he said.
"If there is no progress made, we would want a commission of inquiry into Fiji," Mr Anthony said.
"Should that happen, the government's standing internationally will be seriously in trouble and there will be other repercussions.
"We hope to bring as much pressure as we possibly can on this government to understand that it has certain international obligations."
The ILO had assured the congress it would send a mission to Fiji, Mr Anthony said.
The ball was in the government's court and it had to act now, he said.
"It can't continue parading around the world saying all the right things, but doing quite the opposite when it gets back home."
This is not the first time Fiji has been put on notice by the ILO, Mr Anthony said.
"There was a previous ruling where the government partially acted on its commitment," he said.
"But once the pressure was off, the government decided to take a holiday. So now we've come back to where we were."
Employment Minister Parveen Kumar could not be reached for comment.
But his permanent secretary, Osea Cawaru, had assured the Geneva meeting the government would adhere to agreed reforms.