In a detailed Facebook post Thuku explained that Gachagua issued the directive on April 8 during the memorial service of the late Ol Kalou MP David Kiaraho instructing Mt Kenya residents to accord Ruto respect and avoid insults or disruptions during his appearances in the region.
Thuku said he initially assumed the instruction applied only to that event before realising it covered the entire Mt Kenya area.
Gachagua is now reportedly reconsidering the directive following a wave of attacks on former President Uhuru Kenyatta by Ruto's allies particularly Kesses MP Oscar Sudi.
Thuku warned that if the caveat is lifted the consequences for Ruto's reception in the region could be severe.
"When you come to Mlima we will shower you with the dirtiest words you have ever heard. Zenye zitajishikilia kwa nguo," Thuku wrote painting a picture of an angry reception that would mark a sharp departure from the restrained welcome Ruto has received under Gachagua's guidance.
Rather than lifting the directive entirely Thuku advised Gachagua to take a more measured approach.
He suggested deploying allies to respond to insults on a tit-for-tat basis rather than removing all restraints at once thereby maintaining some level of control over how the situation escalates.
Gachagua has repeatedly positioned himself as a defender of Uhuru and Mt Kenya interests accusing Ruto of working to divide the region's political bloc.
He has warned Ruto's camp to leave the former President alone and claimed the President would struggle to secure significant support in the area in 2027 without proper respect for its icons.
Political observers say the episode reflects the deepening fractures within the Kenya Kwanza coalition and signals that the era of guaranteed polite reception for Ruto in Mt Kenya may be coming to an end.
The region's political temperature has been rising steadily since Gachagua's impeachment in October 2024.
Ruto's camp had not issued a direct response to Thuku's post at the time of reporting.