Tesla CEO Elon Musk said Wednesday that the car company would no longer accept bitcoin to purchase its vehicles, citing concerns about the environmental impact of the cryptocurrency.

“We are concerned about rapidly increasing use of fossil fuels for Bitcoin mining and transactions, especially coal, which has the worst emissions of any fuel,” Musk said in a statement posted to his Twitter account.

Musk later added a chart based on data from the University of Cambridge Centre for Alternative Finance showing what he called the cryptocurrnecy’s “insane” energy usage trend.

The announcement comes a little more than three months after Tesla first announced it would begin accepting bitcoin as payment. The company also said at the time that it had purchased $1.5 billion worth of bitcoin.

The value of bitcoin declined sharply after Musk’s tweet, dropping from about $54,700 per coin to as low as $46,000 before rebounding slightly.

Musk, one of the world’s richest people, said in the statement Wednesday that the company would not be selling any of its bitcoin and intends “to use it for transactions as soon as mining transitions to more sustainable energy.”

He added that the company is also looking at cryptocurrencies that use less energy.

Bitcoin and other cryptocurrencies rely on computing power for their distributed networks, creating a decentralized system to create and track digital assets. But as cryptocurrencies have continued to gain attention, use and popularity, that computing power has become the subject of scrutiny from critics who say they are now significant contributors of carbon emissions.

Musk has pitched Tesla’s electric vehicles and energy infrastructure as a major step forward for reducing carbon emissions. As host of the most recent “Saturday Night Live” episode, he plugged the company’s efforts to reinvent electric cars.

But he has also been a strong proponent of cryptocurrencies, particularly bitcoin and dogecoin, both of which have shot up in value in recent years.

The announcement was a rare reversal from Musk, who has fashioned himself in recent years as a person who courts controversy and rarely gives in to public pressure.