He reminded them that they are all exercising executive powers delegated to them by the President, and their principal was now dropping it.
"Consequently, you are personally responsible for any breach of the legal and policy provisions governing the exercise of your powers in the use of public resources," Koskei wrote.
The warning came in the wake of firing of the first Kenya Kwanza presidential appointee, former PS Josephine Mburu over the Kemsa mosquito nets scam.
It also came on the day another PS - Esther Ngero- made history as the first in this administration to quit, days after being transferred from the Prime Cabinet Secretary office to Correctional Services Department under the Interior Ministry.
The official explanation accorded for Ngero's exit was "personal reasons." Reports have since emerged of fierce fight for control of accounting roles in ministries.
"You are strongly advised to take special note of the specific constitutional and legislative provisions relating to each of your offices and to ensure compliance within your respective institutions. The President expects unwavering fidelity to the Constitution and to the people, on whose behalf you are managing public resources," the memo reads.
He reiterated that "those in charge of managing public resources will take personal responsibility for any loss or misuse of resources."
"Let it be appreciated that those of us who have been honored with the privilege to serve bear a proportionately greater responsibility for the prosperity of the nation and the well-being of its people," the terse memo copied to the Auditor General, Public Service Commission and Ethics and Anti-Corruption Commission says.
He said the President expects the officers to individually and collectively lead the fight against corruption by example, and to bring dignity and honor to the government. He asked them to rally people working under them to appreciate the president's commitment to fight graft.
Koskei also noted that there are adequate legal and policy provisions covering the management of public resources. He said there is therefore no excuse, other than blatant disregard of the law.