Tension is mounting over a new currency rule that, if enforced, many fear could cripple oil and gas companies operating in the Central African customs and monetary union known as Cemac.

The rule will affect companies in countries using the Central African CFA franc (XAF) — Cameroon, Chad, Gabon and Congo-Brazzaville, all former French colonies and prolific oil producers.

Also in the cross-hairs is Equatorial Guinea, a Spanish-speaking state within the Economic & Monetary Community of Central Africa (Cemac) that in 1985 adopted the XAF, a currency governed by the Bank of Central African States from its headquarters in Yaounde, Cameroon.