Ofgem has also stated that the investigation is separate to its probe of the energy supply markets, which started two months ago.
However, SSE has released a statement saying it is confident that its actions in the market "have always been justifiable".
The company has also stated it will "cooperate fully" with Ofgem throughout the process "to bring it to a speedy conclusion".
At the start of this month, SSE became the final of the 'Big Six' energy suppliers in the UK to increase its prices.
The company increased the cost of its gas and electricity by 15.8 per cent and 14.2 per cent respectively.
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