Nigeria's attorney general exceeded his powers in demanding $2-billion in taxes and charges from MTN Group, the telecoms firm said in papers filed with Nigeria's High Court and reviewed by Reuters.
The papers, filed on Monday in a move by the Nigerian arm of the South African firm aimed at potecting its assets, also showed MTN was seeking 3-billion naira ($10-million) from the West African country in court and legal expenses.
Earlier this month, the Nigerian government handed Africa's biggest telecoms company a $2-billion tax bill days after the central bank, in a separate move, ordered MTN's Lagos unit to hand over $8.1-billion that it said was illegally sent abroad.
Nigeria, which accounts for a third of MTN's annual core profit, is MTN's biggest market. Some analysts see politics as a factor in the pressure on MTN as Nigerian President Muhammadu Buhari, who took office in 2015 on promises to push through tougher regulation, is seeking re-election in 2019.
"The attorney-general of the federation (of Nigeria) acted illegally, unconstitutionally, and in excess of his powers" by implementing charges in a "self-assessment exercise" that related to customs, the inland revenue and import duties, the court documents state.
The attorney general's spokesman did not immediately respond to phone calls and a text message requesting a comment.