Nathalie Drouin, the prime minister's national security and intelligence adviser, is scheduled to appear today at a federal inquiry into foreign interference.
The commission of inquiry will also hear from Privy Council clerk John Hannaford, the country's top public servant.
They will testify alongside senior Privy Council official Daniel Rogers, former Privy Council clerk Janice Charette and former national security adviser Jody Thomas.
Later in the day, Zita Astravas, who was once chief of staff to the public safety minister, is expected to appear.
She is likely to be asked why ministerial approval of a specific spy service warrant took longer than usual in 2021.
The inquiry's latest hearings are focused on ways to detect and counter foreign meddling.