Mr Idoko, a lawyer from Kogi State, worked with the Securities and Exchange Commission (SEC Nigeria) before retiring in 2006 as a director.
It was not immediately clear if Mr Idoko’s removal had anything to do with allegations of corruption levelled against him by the staff union.
The IST is an independent, specialised judicial body, originally established under Section 224 of the now-repealed Investments and Securities Act (ISA) No. 45 of 1999.
It is currently governed by Section 274 of the Investments and Securities Act No. 29.
PREMIUM TIMES learnt from a reliable source close to the tribunal that his successor, Jude Udunni, announced his resumption of office at a staff meeting on Friday.
Aggrieved workers of the tribunal had petitioned the Economic and Financial (EFCC), accusing Mr Idoko of corruption.
The committee set up to investigate the allegation completed its work without finding anything against him.
However, a letter signed by the Permanent Secretary of the Federal Ministry of Finance, Mahmoud Isa-Dutse, asked Mr Idoko to handover over to the most senior member of the tribunal.
The chairman was appointed in 2017 along with nine other members after the tribunal was kept idle for two years without any activity.
He was among the full-time members, which included Jude Udunni, Nosa Osemwengie, Abubakar Ahmed and Albert Otesile.
The part-time members included Emeka Madubuike, Kasumi Kurfi, Edward Ajayi, Onyemachi Elujekor and Mamman Zargana. The new chairman would serve in an acting capacity until further notice.
The tribunal has specialized knowledge of the capital market/securities and pension’s law and operations due to the varied technical and operational skills of its members and staff it uses in deciding each case brought before it.