The new law has been challenged by some tribal Senators in Islamabad High Court.
A presidential ordinance enacted on Wednesday night gave each tribal senator one vote instead of the previously allowed “as many votes as the number of vacant seats”.
The critics of the new law saying they will not accept the ordinance enacted in midnight.
“The government has violated our rights to get its candidates winning in polls,” some of them said.
The FATA MNAs have challenged the Presidential ordinance in Islamabad High Court (IHC).
The court has sought reply from the federal law ministry and the election commission over the matter within one week.
According to reports the tribal MNAs have been divided in two groups.
The election commission has suspended electoral process for the four vacant seats of the upper house from the tribal areas due to legal complications.
According to election commission officials the new ordinance have ambiguities and the commission officials trying to understand it.
The commission has sought the opinion of the law ministry about the new ordinance, which was signed by the President into law, a day before the Senate elections.