Kazakh authorities have fined Chevron $609m (£298m) for alleged environmental lapses, the latest in a number of moves against foreign investors.
Officials said there were a host of environmental errors at the Tengiz oilfield. Chevron has yet to comment.
The business climate in Kazakhstan has become more uncertain amid a row over the foreign-operated Kashagan oilfield.
Kazakh MPs recently approved a law allowing the government to break contracts with foreign firms.
'Systematic violations'
The move, which has yet to be approved by Kazakhstan's president, threatens to undermine existing commercial deals in the oil-rich country.
Unease has grown about Kazakhstan's attitude to foreign investment since it demanded huge compensation from the foreign consortium running the Kashagan oilfield for production delays and spiralling budgets.
Ministers said the Chevron fine was for "systematic violations", including many which they said had gone unreported for several years.
"Any company that does not fulfil ecological requirements will be dealt with in the harshest way," said energy minister Sauat Mynbayev.
^ Back to top | BBC Sport Home | BBC Homepage | Contact us | Help | ©
~RS~q~RS~~RS~z~RS~52~RS~)