South Africa’s economy will face a price hike by Sasol for gas supply that will add about R325 million ($20 million) a month to the cost, according to an association of users of the fuel.

“The current gas pricing uncertainty holds risk” for the biggest buyers, the Industrial Gas Users Association of Southern Africa said in a statement Wednesday, referring to a 96% price increase that took effect August 1.

Sasol delivers gas it produces in Mozambique through the Rompco pipeline to its own operations as well as to consumers.

The National Energy Regulator of South Africa (Nersa) last week said it had been alerted to “imminent excessive increases in gas prices” by one of its licensees, which it didn’t identify, and would investigate any unreasonable pricing.

The price was determined by using a methodology approved by Nersa, it said.