Ukraine has changed the charter of Naftogaz in violation of a deal with foreign creditors, according to reports.
The move could hold up a $500million loan for vital gas purchases from Europe, the state-run energy firm said in a statement.
A spokesman for Naftogaz said the funds are essential for gas purchase and will allow Ukraine to get through the winter season in a “stable manner”.
Concern was expressed by the European Bank for Reconstruction and Development over the move.
Naftogaz said the economy ministry had transferred control of the company’s gas transport arm last week, in violation of corporate governance principles.
Since December last year, Ukraine has not bought any gas from traditional supplier Russia, instead importing gas from Europe.
Prior to that in October, the government had approved plans to reform the corporate governance of Naftogaz in exchange for loans worth $800million from the World Bank.