Tesla CEO Elon Musk stated on Sunday that the company will resume accepting Bitcoin as payment for its electric cars once it confirms that there is a “reasonable” level of clean energy used by miners.

CNCB reports that Tesla CEO Elon Musk stated on Sunday that the company will resume Bitcoin transactions once it confirms that there is a reasonable amount of clean energy used by Bitcoin miners. Musk stated: “When there’s confirmation of reasonable (~50%) clean energy usage by miners with positive future trend, Tesla will resume allowing bitcoin transactions.”

Musk’s comments came in response to a statement from Magda Wierzycka, the CEO of South African asset manager Sygnia, who said that Musk’s tweets on Bitcoin prices were “market manipulation” and should have resulted in an investigation from the U.S. Securities and Exchange Commission.

Tesla revealed in an SEC filing in February of this year that it purchased $1.5 billion worth of Bitcoin and said that it would begin accepting Bitcoin as a payment method for its vehicles. But, Tesla halted car purchases with Bitcoin in May due to concerns over cryptocurrency mining and the energy usage it requires contributing to climate change.

“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 May. On Sunday, Musk disputed claims by Wierzycka that he was attempting to manipulate the price of Bitcoin, stating that: “Tesla sold roughly 10% of its bitcoin holdings to confirm BTC could be liquidated easily without moving market.”

During the first quarter, Tesla sold $272 million worth of “digital assets” which helped to reduce operating losses by $101 million, according to the firm’s earnings statement. Musk’s latest comments about Bitcoin coincided with the cryptocurrency’s price rising by around eight percent.