The True Way was a Cardassian terrorist organization that operated in the 2370s. They believed the Federation to be the greatest threat to the Cardassian people, and the cause of the Cardassian Union's economic and political difficulties. Until 2372 they had never committed any acts of terrorism against the Federation or Bajor.
The True Way reemerged in 2376, where they tried to destabilize the new Cardassian government. Elim Garak revealed that he once joined the group to spy on them. (DS9 Pocket: Worlds of Star Trek: Deep Space Nine, Volume 1)
The True Way emerged once more in 2383 to denounce the resurgence of the Oralians, a religious group that dated back to the Hebitian civilization and was previously outlawed. By 2409, they had become deeply rooted in Cardassian space, waging a campaign of terror and fear throughout the region in an attempt to expel the Federation, and to return Cardassia to its old ways. (Star Trek Online)