Nigeria Communications Commission spokesman Reuben Muoka said the call quality of the four companies were poor and they also delivered poor services leading to the imposition of USD 7.3 million fine on them.
The affected companies are Nigerian subsidiary of Bharti Airtel 'Airtel Nigeria', South Africa's MTN, Abu Dhabi's Etisalat and local Globacom. Bharti Airtel officials could not be reached for comments.
The telecom regulatory authority had earlier in October 2011 warned the firms to improve their services or face sanctions, Muoka said.
A statement by NCC said poor performance in March and April attracted the penalty. It said the firms' poor performance was noticed in January and February, adding that a grace period was added to enable them make some improvements but they failed to do so.
According to the reports, while Airtel faces a penalty of USD 1.68 million, Etisalat and MTN will have to pay USD 2.25 million each and Globacom faces a penalty of USD 1.125 million. Poor services by these companies make it difficult to receive or make calls in Nigeria.
Their data services are equally poor. Many Nigerians prefer to carry more than one phone so they could have an alternative connections when one fails, officials said.