The diplomatic flap over undocumented migrant workers in Malaysia, and the failure of erring Malaysian employers to pay the wages due to them before a crackdown that began on Tuesday, could have been avoided, unionists say, had these workers been encouraged to join local trade unions.

This is among a host of issues that Malaysia's rejuvenated labour movement will have to grapple with after watershed elections for top posts in the country's umbrella trade union body swept in a new reform-minded leadership.

Malaysia arrested more than 550 foreigners, mostly Indonesians and Filipinos, as the sweep against an estimated one million undocumented migrant workers entered its second day on Wednesday following the end of a four-month amnesty that allowed around 400,000 illegal migrants to leave without punishment.