One of Hong Kong’s leading pro-democracy campaigners has fled the territory over fears that he would be under constant threat of arrest after China imposed its controversial national security law. Nathan Law, a former lawmaker and leader of the 2014 Umbrella Movement, said late Thursday that he felt forced to leave Hong Kong because he faced “unknown dangers” now that the new law has taken effect. His announcement came shortly after he spoke to a U.S. Congressional panel via video link. “After I spoke at the hearing and told the international community about the real human rights situation in Hong Kong after the draconian law took effect, I have plunged myself into unknown dangers,” he wrote on Facebook, adding: “Now we have to think of how to continue our front line and to keep the flame alive under the most violent suppression.” On Friday, the Hong Kong government reportedly announced that the use of a popular protest movement slogan—“liberate Hong Kong, revolution of our times”—was now illegal under the national security law.