In the letter, the groups termed the claims as "treacherous" and expressed concern that MPs are involved in a scheme to spread misinformation about the impact, utility and focus areas of the funds in Kenya.
"Their action may result in PEPFAR funding being discontinued in Kenya which would jeopardize the lives of over 55 million Kenyans who benefit from HIV programmes supported by PEPFAR as well as more than 1.6 million people living with HIV in Kenya," read part of the letter.
Rettmann further said there is however need for all development partners to realign their programmes to go beyond HIV prevention and treatment in line with President William Ruto's UHC agenda.
This he said will ensure Kenya sustains itself in terms of financing such programmes in the years to come.
"For the last 20 years Kenya has done tremendously well in terms of suppressing the virus, Currently, there are about 1.3 million people with HIV who are on treatment. This represents 94 per cent of the total population that is living HIV," he said.
According to him, with such initiatives like Pepfar had played a key role in reducing the rate of new infections and deaths.
"We have moved from the days when HIV/AIDs was a pandemic and many people would die due to despair and now we are at a stage where people are living and with it and can live for the rest of their lives with just a pill a day," said Rettmann.
According to him, they have so far spent over 8 billion dollars in trying to bring as many people as possible to start treatment.