Siegfried Wolf, the new chairman of state holding company OIAG – the biggest shareholder in Telekom Austria – said the surprise €400 million writedown of the operator’s Bulgarian unit put it in “an extremely precarious situation”.

Speaking to News magazine, and picked up by Reuters, Wolf said there was an “absolute need to clear up seamlessly how it could come to such a writedown from May to mid-June”.

He added that neither financial markets nor shareholders like bad surprises. “This kind of thing cannot be allowed to happen again,” he said.

The impairment charge, said Reuters, will push Telekom Austria to a near-certain 2014 loss.

Telekom Austria, on announcing the writedown, said in a statement that the impairment was “primarily due to an increase in the cost of capital of the Bulgarian segment and changed expectations with regard to medium-term macroeconomic developments in Bulgaria, as well as related market effects which affect the valuation of Telekom Austria Group’s business plan for the Bulgarian segment”.

At the time of the impairment charge, Hannes Ametsreiter, Telekom Austria CEO, said he hadn’t received any negative comments from shareholder América Móvil, which is on the verge of taking over the Austrian incumbent.

Wolf, too, said America Movil had taken the writedown news “very professionally”.