The ODM leader said it is "an established fact that once GMOs are introduced, it is virtually impossible to stop their transfer to where natural crops are grown because of wind and insect pollination."
"Ruto is not working to promote Kenyan research work in Kenyan universities, colleges and institutions. He is working to promote foreign biotechnology institutions abroad," he said.
"In other words, GMOs can completely wipe out native and natural crops leaving Kenyans dependent on seeds and foods produced by GMO multinationals."
Raila asked the government to immediately reverse its decision on importation of GMO foods until Kenyans have a robust debate on the matter.
He said the science on GMO foods and farming was at best extremely controversial and at worst incomplete. He said there was no scientific study thus far that has unequivocally cleared it as fit for human consumption and the environment.
The ODM leader said the studies that have come close to giving GMOs a clean bill of health are generally those sponsored by biotechnology companies themselves or their associates.
"We challenge the government to share with Kenyans the scientific study it is relying on to declare GMO maize as fit for our consumption and our environment. GMOs can cause harm to human and animal life and to the entire national ecosystems. They can dramatically reduce or eliminate plant diversity," said Raila.
Trade, Investment and Industry Cabinet Secretary Moses Kuria on Friday said he will allow the importation of GMO and non-GMO maize into the country to cure the current shortage.
"We will allow for the importation of duty-free maize until the country achieves food security and until we are satisfied that there is enough maize in the country," Kuria said.
The move follows the Cabinet approval of the use of GMO foods in early October, rescinding the ban that was put during the former President Mwai Kibaki's administration.
Raila said after hurriedly lifting the ban on GMO foods, the UDA administration has now authorised the duty-free importation of 10 million bags of genetically modified maize for at least six months.
"We in Azimio la Umoja want to state categorically that this decision - which has been made without deliberation or public participation - will have far-reaching and catastrophic implications for Kenya's agriculture, the health of the Kenyan people and our environment," said Raila.
The former Prime minister said GMO foods posed a direct threat to Kenyans' health, farmers, soils, institutions and seeds.
"GMOs are a new form of colonialism that will leave us permanently at the mercy of malign foreign nations and greedy corporations. Simply put, GMOs are an existential threat to Kenya's food systems, ecosystems, and its human and plant life," he said.
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He said in most democratically and scientifically advanced countries, the question of GMOs remains one of the greatest public concerns and controversies
Raila said many countries in the European Union have banned GMOs. He listed France, Germany, Austria, Greece, Hungary, The Netherlands, Latvia, Lithuania, Luxembourg, Bulgaria, Poland, Denmark, Malta, Slovenia, Italy, and Croatia as some of the counties that have banned GMOs.
In Africa Algeria and Madagascar have banned GMOs. Turkey, Kyrgyzstan, Bhutan, and Saudi Arabia having also disallowed the science and in Americas, he listed Belize, Venezuela, Ecuador, Peru and Venezuela.
"What does the UDA regime know that these leading countries on the global stage that have banned GMOs do not know? What is this regime's interest in GMOs? In the present circumstances, we call upon our two Houses of Parliament to stand up for the people. Parliament must push for motions to comprehensively and fully debate what the country should do with GMOs," said Raila.
He appealed to the people's representatives to lead this discussion with immediate effect and invite Kenyans from all walks of life to submit their views, adding that this was a matter of grave national importance and cannot be decided in "secrecy and opacity" by the Cabinet without the input of the people.
"We note with alarm the callousness with which the UDA regime in the person of Trade CS Moses Kuria announced the pending importation of GMO maize. With utter contempt for the Kenyan people, Kuria publicly said that since there are a thousand ways for Kenyans to die, the safety of GMO foods should not worry us because we are dying anyway," said the ODM leader.