Deputy leader Christian Engström told The Local that the Pirate Party believed the new law was in clear breach of the European Convention for the Protection of Human Rights and Fundamental Freedoms.
The new legislation, set to take effect on January 1st 2009, will enable the National Defence Radio Establishment (FRA) to monitor all email and phone calls crossing Sweden's borders
"The European Convention is built into the Swedish constitution, and the new law goes way beyond what is permitted under Article 8," he said.
The article referred to by Engström states that:
"Everyone has the right to respect for his private and family life, his home and his correspondence."
"There shall be no interference by a public authority with the exercise of this right except such as is in accordance with the law and is necessary in a democratic society in the interests of national security, public safety or the economic well-being of the country, for the prevention of disorder or crime, for the protection of health or morals, or for the protection of the rights and freedoms of others."
Christian Engström said he was in little doubt as to the eventual outcome of a court battle.
"I'm confident Sweden will lose the case, but the process is likely to take a long time.
"For now the most important thing is to ensure people remain angry about this." he said.
Next summer's European Parliament elections would be an interesting litmus test for the level of popular disaffection with the government, said Engström, who concluded by paraphrasing Winston Churchill:
"This is just the end of the beginning," he said.