A Parti Amanah Negara (Amanah) lawmaker has questioned why the Inland Revenue Board (IRB) is not probing Prime Minister Najib Abdul Razak's stepson Riza Aziz as well as Youth and Sports Minister Khairy Jamaluddin.

Kuala Terengganu MP Raja Kamarul Bahrin Shah Raja Ahmad raised this issue in the wake of IRB raiding companies belonging to Dr Mahathir Mohamad's sons.

"Riza is really young to have such wealth, compared to other veteran businesspersons who have been in the corporate world a long time.

"Is this (the absence of a probe) because Khairy is a cabinet minister and Riza is from a family group who is still in power, so they have invincibility in the eyes of certain authorities?

"Why are they being selective and only target those from families who are no longer in power?" he asked during a press conference in Parliament this morning.

Khairy, who is also Umno Youth chief, is the son-in-law of former premier Abdullah Ahmad Badawi.

Raja Kamarul also questioned whether IRB is zeroing on Mahathir's sons due to pressure from Deputy Prime Minister Ahmad Zahid Hamidi as well as Tourism and Culture Minister Nazri Abdul Aziz.

"Is it just a coincidence or did IRB receive pressure from Umno?" he asked.

Last week, there were calls from Umno ministers to probe the wealth of Mahathir's children after the latter claimed that Zahid failed to provide a clear answer on the RM230 million in his account when he declared his assets to the former premier in 1996.

Zahid said that he is willing to be investigated, and claimed that his wealth was acquired during his time in the corporate sector.

Meanwhile, Raja Kamarul, in an obvious reference to 1MDB, accused the IRB and Malaysian Anti-Corruption Commission (MACC) of ignoring the "elephant in the room".