New labour regulations aimed at making it harder to retrench workers in Zimbabwe came into force on Wednesday, a legal watchdog said.

That meant President Robert Mugabe, 91 has signed the amendments that were hastily passed by both houses of parliament last week.

Legislators were recalled from recess to pass the amendments, promised by Mugabe after a surge in job losses from mid-July.

Not less than 20,000 to 25,000 Zimbabweans lost their jobs in the last month and this ugly trend was observed in both private and state-run firms. It was sparked by a Supreme Court ruling that redundancy pay-outs were not obligatory and employers wanting to fire workers had only to give three months' notice.

That has now changed, according to a copy of the new Act provided by Veritas Zimbabwe.

Retrenchments are now only allowed under certain circumstances and a minimum retrenchment package of one month's pay for every two years served is payable.

Some lawmakers from the opposition Movement for Democratic Change (MDC) had wanted bigger pay-outs to be imposed.

But employers have warned the new regulations may force companies to shut down.

The amendments have been backdated to July 17, meaning employers who have retrenched since then will have to fork out for pay-outs they thought they'd avoided.

Lawyers had warned against backdating the changes, saying this will spark court challenges from employers.

There are unconfirmed reports that some firms are now rehiring workers they had retrenched in the last few weeks to avoid the retrenchment costs they hadn't budgeted for, according to the Sunday Mail newspaper.