Rafizi Ramli has responded to former premier Najib Abdul Razak's warning to Putrajaya that imposing Capital Gains Tax (CGT) on the sale and purchase of shares would be detrimental to the nation.

"I do not know what new taxes (the government) would introduce. I authored the alternative budget from 2011 and suggested that profits from shares be taxed using CGT.

"Imposing a tax on profits from shares is fairer than GST," he added in a Twitter posting this afternoon.

The former PKR lawmaker said at present, investors and global fund managers reap profits from the sale and purchase of shares without having to pay tax.

"I am not sure how much (can be collected) from the new tax on share profits but based on principle, these profits must be taxed," he added.

The GST which was introduced by the previous administration has since been replaced with the SST.

In a Facebook posting earlier, Najib said imposing CGT on the sale and purchase of shares would drive foreign and domestic investors to other markets, which do not have such a tax.

Prime Minister Dr Mahathir Mahathir had urged Malaysians to prepare to sacrifice with regard to the implementation of new taxes.

Following this, Finance Minister Lim Guan Eng said Malaysians must be prepared for "pain and sacrifice" due to new taxes to be introduced in Budget 2019.

Neither mentioned CGT, although some news articles have suggested that it would be a good move to generate revenue.