Hong Kong’s pro-democracy lawmakers said Wednesday that they would resign en masse to protest Beijing’s growing control over the local legislature, one of the last remaining centers of dissent in the Chinese city.

The 15 resignations were set off by a decision earlier in the day out of Beijing that forced the removal of four opposition lawmakers in Hong Kong.

The lawmakers’ departure comes amid Beijing’s intensifying efforts to silence Hong Kong’s political opposition and to curb a vast protest movement.