(CNN) A coalition of civil society groups has launched a lawsuit to block the purchase of luxury cars for principal officers in the Nigerian Senate.

The activists said in the lawsuit that spending such an amount on cars in Nigeria's present economic state was "unjust and fair" and contradicts their oath on taking office to prioritize the welfare of citizens.

The class action was brought forward by the Socio-Economic Rights and Accountability Project (SERAP), BudgIT and by 6,721 Nigerians including Bring Back our Girls campaigner and former presidential candidate Oby Ezekwesili.

"They can have official cars but why would they spend such an amount buying cars for 109 Senators when more than half of Nigerians are living in abject poverty," the group's spokesman Kola Oludare told CNN.

Opponents of the idea says 5.550 billion naira would be spent, which converts to around $15.3 million in US currency.