May 27 (Reuters) - Tech billionaire Mike Cannon-Brookes is seeking two seats on AGL Energy's board, if the Australian power producer's plan to split into two companies fail.

In the letter addressed to AGL Chair Peter Botten on Friday, Cannon-Brookes reiterated that the demerger was a 'deeply flawed' plan and expressed his intention to appoint two nominees for Grok Ventures - a vehicle he owns - on the board of AGL.

"We intend to engage directly with you and your fellow AGL Directors in relation to board and management renewal. We want to ensure that AGL has the talent, capital, capability and oversight that is required to embrace the opportunity presented by decarbonisation," according to the letter.

Cannon-Brookes, the co-chief executive officer of software firm Atlassian and a vocal climate activist, gained an 11.3% stake in AGL earlier this month by converting a part of his derivatives-based holding in the company, having failed in a takeover attempt with Brookfield Asset Management earlier this year.

The letter follows an announcement from Australian pension fund HESTA, which joined the tech billionaire in opposing the demerger, saying it does not see the split supporting decarbonisation targets laid out by the Paris climate agreement.

Shareholders are set to vote on June 15 on AGL's demerger plan. The split will form AGL Australia, which will be the country's top energy retailer, and Accel Energy, the country's top power producer.

Accel will inherit AGL's coal-fired power plants and the mantle of Australia's largest carbon emitter, according to government data.

(Reporting by Tejaswi Marthi in Bengaluru; Editing by Rashmi Aich)