Elliott Investment Management LP is calling on Houston-based utility giant NRG Energy Inc. to upend its strategy because of “operational and strategic mishaps.”

The activist investor, which said it has spent $1 billion to secure a 13% stake, sent a letter on Monday to NRG’s board specifically criticizing a $2.8 billion deal to buy home technology company Vivint Smart Home Inc. The purchase, which recently was completed, was not aligned with NRG’s strategy, according to Elliott.

Elliott in a letter and materials sent to the board, said it was presenting “a clear path forward for how best to remedy NRG’s meaningful underperformance and create significant and sustainable value.”

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