National Super Alliance (NASA) leader Raila Odinga is set to be sworn in on December 12 and has been urged by various leaders not to go ahead with his plans.
Veteran politician Koigi Wamwere penned a letter to the Opposition leader asking him to use constitutional means to push for reforms in the country.
Koigi stated that Odinga must have been pushed by some leaders to agree to be sworn in because he was not for the idea initially.
"Brother Raila, I agree with your hesitancy to be sworn in as president, which you expressed at the Nasa meeting in Maanzoni, Machakos County.
"But I know some people called you a coward and urged you to agree to be sworn in. But I know you have never been cowardly," wrote Mr Wamwere.
He warned the NASA leader that being sworn in would lead to war and his 'shadow presidency' would cause a scare.
"If you are sworn in, our dear land will have two presidents, two governments and will be in a state of war.
"Kenya will be in a state of war because no country can have two armies and have peace and no country can have two presidents and not be at war.
"And while your presidency will not have the legal power of the Uhuru presidency, it will be a shadow presidency that can still scare," stated Wamwere.
The veteran politician further stated that if Raila is sworn in without the force of law and Constitution, Kenya will have two governments and two presidents, with one side armed and the other unarmed.
"If we allow Kenya to slip into a war like it happened in Biafra and Rwanda, resulting in the deaths of millions of people, we shall bear joint and collective guilt of our collective conscience because we could have stopped this," he reiterated.