KUALA LUMPUR - An anti-hopping law (AHL) crucial to Prime Minister Ismail Sabri Yaakob's stability is facing 11th-hour doubts from Malaysia's opposition, whose support is required to reach a two-thirds supermajority in Parliament for a constitutional amendment.

The Straits Times has learnt that main opposition pact Pakatan Harapan (PH) is unhappy with the unclear language in the amendment, to be tabled in a special sitting on Monday morning (April 11), and has sent an alternate version to the government.

"We want to specify defections. We expect the government to counter our draft but as long as defections are clearly defined, we can consider it," a lawmaker involved with the negotiations said on the condition of anonymity as these are confidential.

Implementing anti-hopping measures is a crucial plank in the confidence-and-supply agreement (CSA) inked between the Ismail administration and PH in September, which bars the Premier from dissolving Parliament until August.

Should PH void the accord due to an unacceptable AHL, it would open Datuk Seri Ismail to a withdrawal of support from colleagues in his government, which has only a slim majority of 114 out of 220 MPs.

The government has said the constitutional amendment to be debated on Monday and Tuesday is to have an "enabling clause" so that an anti-hopping Bill can be tabled that does not run contrary to existing provisions for freedom of association.

But Mr Ismail said on Sunday that the Bill will be tabled only in July, despite PH demanding the legislation be approved "as soon as possible".

PH has said it will give fulsome support to the AHL but delays and any attempt to water down measures contained in the legislation could hurt its standing among voters, some of whom have already accused opposition leader Anwar Ibrahim's coalition of propping up an Umno-led regime.