The Trade and Office Union (Handel og Kontor - HK), part of the umbrella organization LO, said on Wednesday that the report still left many questions unanswered.
"We have a number of concerns that are unanswered, including whether there is a culture of fear and if (Ryanair) violates freedom of association," the union wrote on its homepage.
In a letter addressed to the Air Traffic Agency, HK has asked for information about whether Ryanair bosses were present when the state authority's agents interviewed employees in Norway.
"If that is the case, their report is not worth much," HK chairwoman Trine Lise Sundnes told the newspaper Aftenposten. "Furthermore, we reacted to the fact that the report did not address that people have lost jobs when they have taken up union work."
Ryanair has been drawn into a long-standing battle with Norwegian authorities, which went so far that Labour Party Prime Minister Jens Stoltenberg publicly said he would never travel with them. Ryanair boss Michael O'Leary visited Norway in April to reject accusations that his low-cost airline treated its employees like slaves, as unions and politicians in the Scandinavian state called for a boycott of the firm. His trip came as two former stewards prepared to sue the Irish carrier for unfair dismissal and breaching labour laws.
"It was a contract of slavery," Vegard Einan of the Parat union, which assisted the two women in their lawsuit, told the AFP news agency.
O'Leary, speaking to reporters at Rygge airport during his visit, said that his firm fully respected European legislation and that he was the victim of "a series of false claims".
The Norwegian Air Traffic Agency (Luftfartstilsynet) reported on Tuesday that while it found no gross work environment abuse by Ryanaire, the Irish budget carrier had to submit more information and had until November to get its job contracts in line with Norwegian regulations. The agency said that Ryanair had until November 1st to ensure that employment contracts for its staff in Norway falls in line with laws governing working hours in Norway. If amendments are made before then, the airline will not risk a fine.