Hong Kong (CNN)The ramifications of a new security law imposed on Hong Kong by China are still unfolding, as authorities moved to outlaw a popular protest movement slogan and at least one prominent activist fled the city rather than face potential arrest.

Nathan Law, a former lawmaker and leader of the 2014 Umbrella Movement, said late Thursday that he had left Hong Kong, soon after speaking to a US Congressional panel via video link. Law said he knew speaking to lawmakers in Washington about the law would put him in its crosshairs, at it bans “collusion” with foreign powers.
“The choices I have are stark: to stay silent from now on, or to keep engaging in private diplomacy so I can warn the world of the threat of Chinese authoritarian expansion,” he said. “I made the decision when I agreed to testify before the US Congress.”