Prime Minister Najib Abdul Razak needs to read properly before claiming that Pakatan Harapan supports the goods and services tax (GST) too, said opposition leader Dr Wan Azizah Wan Ismail.

"He (Najib) didn't read properly. We know that all the GST instruments are already in place, so if we stop it suddenly, it could be seen as irresponsible.

"So what we did was (we made GST) zero rated," she told reporters when met after Najib tabled Budget 2016 in the Dewan Rakyat.

In its alternative budget, Pakatan Harapan said it would "effectively abolish" the GST by making all goods and services zero rated.

In his budget speech, Najib however said the opposition were in favour of the GST.

"Those on the other side who at first vehemently opposed it, now accept GST and have included it in their budget.

"This shows that the opposition's stance always changes and is inconsistent," he said.

In the 2016 budget, Najib announced that more items would be GST exempt including medicines, baby formula, and mee kolok.