69-year-old Rajapaksa has been asked to appear before the Commission to Investigate Allegations of Bribery or Corruption (CIABOC) on April 24.
The former President is to be quizzed by the anti-graft commission over giving a ministerial portfolio to then opposition legislator Tissa Attanayake.
Rajapaksa is accused of paying the senior member of the opposition to defect shortly before January's presidential election, in which he was defeated by one-time ally Maithripala Sirisena.
Since coming to power, Sirisena has launched a series of investigations against Rajapaksa's inner circle into allegations of corruption. But this will be the first time the former President himself will face questioning.
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Protesting the summoning of Rajapaksa, his loylists today staged a demonstration in Parliament, forcing Speaker Chamal Rajapaksa to adjourn the sessions until tomorrow.
They sat in the well of the chamber urging the Speaker, who is Rajapaksa's elder brother, to intervene in the the matter.
Lakshman Kiriella, the Leader of the House, said the government was unaware of Rajapaksa's summoning and the Commission had acted independently.
"If you have a problem with it, you can take a legal action against the Commission," Kiriella said.
The ex-president's aide had earlier told media that Rajapaksa will seek legal advice before reporting to the commission.