BANGKOK, March 20 (Xinhua) -- Thai senate speaker Nikom Vaiyaratpanich was legally forced to stop performing as head of the upper house on Thursday, pending possibilities of being impeached at a later date.

The National Anti-Corruption Commission reached a unanimous decision to immediately stop Nikom from performing and to call on the senate to subsequently impeach him for allegedly abusing his power during last September's amending of the constitution, which, according to the anti-graft agency, prompted the making of allegedly illegitimate procedures and rules for the composition of future senators.

However, the upper house needs a minimum of three-fifths of all senators to impeach and deprive Nikom of the post of senate speaker for such alleged misconducts.

Last November, the Constitutional Court ruled that the constitution amendment involving the making of future senators was "illegitimate" and "unconstitutional."

The controversial amendment had sought to have all future senators elected by constituents instead of having only one half of them elected by constituents and leaving the other half to be handpicked by members of independent agencies as was the case of the current senators.

Meanwhile, Nikom said he will defend himself from such misconduct charges during a special session in the upper house which is yet to be scheduled so that his colleagues might probably spare him the impeachment.

Deputy senate speaker Surachai Liangboonlertchai has automatically become acting senate speaker.