The board okayed the corruption reference against the Sharif brothers on Wednesday for constructing a two-lane road from Raiwind to their family residence at Jati Umra, which allegedly caused a loss of over Rs 125 million to the national exchequer, the News International reported.
Three corruption references are already pending before an accountability court against the ousted prime minister.
The NAB also authorised investigations against two former Prime Ministers -- Raja Pervaiz Ashraf and Yousuf Raza Gilani -- belonging to the Pakistan People's Party (PPP).
Mr Ashraf will face an investigation regarding a Rs 113 billion loss to the national exchequer caused by the delay in the execution of the Nandipur Power Project and Gilani for misuse of authority in appointments in Saindak Metal Limited.
Balochistan's former chief minister Nawab Aslam Raisani, former Communication Minister Arbab Alamgir and his spouse Asma and senior leader of the Pakistan Tehreek-e-Insaf (PTI) Babar Awan also came under the lens of NAB with the initiation of investigations against them.
Mr Raisani is accused of receiving compensation of over Rs 1,817 million from the Balochistan government, which he allegedly distributed among his relatives.
Mr Alamgir and his wife were accused of having assets beyond their known sources of income. Both had accumulated assets of over Rs 2.486 billion.
The NAB Executive Board's meeting chaired by Justice Javed Iqbal (retd) also decided to launch investigations and filing of references against former law ministry secretary Masood Chisti, former secretary Water and Power Ministry Shahid Rafi and former director Ijaz Bashir for allegedly delaying the Nandipur Hydel Power Project that caused a loss of over Rs 113 billion.
A reference against a former chairman of the Evacuee Trust Property Board, Syed Asif Akhtar Hashmi, was also approved.