Malcolm Turnbull will be asked to appear before an inquiry examining a $443.8m grant to the Great Barrier Reef Foundation.

The Senate inquiry’s chair, Greens senator Peter Whish-Wilson, said on Thursday the committee had resolved to write to the former prime minister and request he give evidence at a future hearing.

Turnbull’s decision to resign from the parliament means he could be compelled to appear if he refuses the invitation.

Turnbull and the then environment and energy minister Josh Frydenberg had a meeting with the foundation’s chair, John Schubert, on 9 April that led to the offer of the controversial grant.

The grant was awarded without a tender process and the foundation has said it did not apply for it.

Documents obtained by Guardian Australia showed no mention of the record grant until 12 April and that Frydenberg’s office and the department had initially been discussing a smaller grant of $5m that was awarded to the foundation for a reef islands project.

The documents also revealed the department warned the government there was a “significant risk” the grant would delay on-the-ground projects.

Labor has argued this showed the decision to award the grant was “clearly wrong”.

Earlier this month the opposition told the foundation to prepare to return any unspent funds if there is a change of government at the next election.

Whish-Wilson has said one of the main purposes of the inquiry is to establish who had the original idea to award the almost half a billion dollar grant.

The next hearings will be held on 18 and 21 September.

Schubert and fellow board members Stephen Greenfield and Grant King have agreed to give evidence to the inquiry next week.