What can be done to prevent Singaporeans from mistreating their domestic workers?

A SilkAir flight attendant was recently jailed for two months for maid abuse. Siti Farhana Mhd Yahkup and her husband, Mohammed Szami At'tirmidzi Supa'at, had hit their maid after they heard their daughter crying. Siti Farhana got angry and held the maid's head and pushed it against the wall several times. She later punched her maid on her chest several times while her husband kicked the maid on her shin. What can be done to ensure domestic workers are treated well?