Nabu says some MPs are part of an organised crime group that was uncovered in an undercover operation carried out by Nabu and Sapo - an anti-corruption unit within the prosecution service. No details of the investigation have been made public, but it is said to be about bribery.
When investigators were to raid parliament on Saturday, they were initially stopped, according to Nabu. But they were later allowed into the heavily guarded building, the security service said on social media.
Ukraine has previously been rocked by a major corruption scandal. Both ministers and President Volodymyr Zelensky's former closest aide, Andriy Yermak, have been forced to leave their posts.
The investigation comes at a critical time for Zelenskyy, who has just traveled to Canada and the United States to discuss the details of a 20-point plan to end Russia's war of aggression.
The corruption scandal has sparked public anger in Ukraine, while Russia continues to attack the country with missiles and drones. However, Zelenskyy continues to enjoy strong support among the population.
