China’s Hong Kong military garrison warned protestors on Sunday that they could be arrested for targeting its barracks in the city with laser lights.

As a few hundred protestors shone laser lights on the barrack walls, troops in fatigues on the roof of the building shone spotlights at protestors and used binoculars and cameras to monitor protesters.

In the first direct interaction between the People’s Liberation Army (PLA) and protesters, the PLA raised a yellow flag with the arrest warning written in large letters, said a Reuters witness.

Authorities are bracing for two major protests on Sunday, fearing a recurrence of Friday night’s violent protests which saw the Asian financial center virtually shut down the next day.