MTN Nigeria is being sued by rival Etisalat over its proposed acquisition of internet provider Visafone, adding to its woes in the country.

Nigeria’s market leader MTN, which is currently embroiled in a legal fight with regulators over a $3.9 billion fine, struck an agreement to acquire Visafone last month.

The deal has, however, attracted the attention of Abu Dhabi-based Etisalat, owner of Nigeria’s fourth largest player, which is taking issue with MTN’s potential use of Visafone’s 800MHz spectrum, as it looks to beef up its mobile data offering.

“Not to challenge will entrench the dominance of MTN in the data services market,” the company told Bloomberg.

According to the publication, MTN was in court last week over the matter.

The Visafone deal has also already been approved by NCC, and a spokesman for the regulator told Bloomberg it hadn’t received anything from Etisalat questioning the decision.

According to GSMA Intelligence figures, MTN is significantly ahead of its rivals in the market, with a forecasted 68.2 million connections as of Q1 2016. Both Airtel and Globacom have 32.8 million, while Etisalat has 25.2 million.