The decision by Chief Justice Martha Koome, judges Mohamed Ibrahim, Smokin Wanjala, Njoki Ndung'u and William Ouko was a big blow to the Council of Governors which has been fighting to stop the Senate from summoning governors.
Governors complained that the Senate summonses were unconstitutional for violating provisions on separations of powers and that in the case of audit queries, it is their County Executive Officers for Finance who should be summoned.
The apex court however ruled that the buck stops with the governors as the county's Chief Executive and that they cannot send any of their representatives including their Ministers for Finance when summoned by the Senate.
"The governors must appear in person when summoned by the Senate," ruled the judges.
"However, when appearing before the senators, there is nothing that stops them from going with a technical team from the County Executive to help in providing the required information."
They added that it is only in a situation where the Senate is of the view that the questions to be answered or information to be provided do not need the personal input of the governor that it may restrict its summonses to the relevant county official or Executive Committee Member.
There is no way by which the Senate can perform its oversight role of ensuring proper usage of public resources in the counties without having the powers to summon a governor to provide answers regarding the management of county finances and related affairs, the judges said.
"Without such power, the Senate would not be able to protect the interests of the counties, nor would it be able to exercise effective oversight role over national revenue allocated to counties," ruled the apex court.
The governors had also argued that the Senate only has powers to look in to matters related to revenue allocated by the National Government and not locally generated revenue which they claimed should be monitored by the county assemblies.
But the apex court overruled them stating that the Constitution specifies only one account for the county government irrespective of the source of funds.
"The fact that county revenue is locally generated does not remove it from the purview of Senate oversight role," they ruled.
"Such revenue still falls within the rubric of public finance whose use must remain under the radar of scrutiny by the State organs established for that purpose."