The Polish Securities Commission is investigating potential insider trading in the shares of utility EC Bedzin SA after the stock’s 952% surge this month caught the eye of Prime Minister Mateusz Morawiecki.

The valuation sky-rocketed without any apparent reason, although the power producer — which denies the accusation — reported in regulatory filings that insiders were buying its shares. On Wednesday, the company said it had signed a non-disclosure agreement with a company co-owned by state-controlled energy giant Orlen SA about talks on the construction of small nuclear reactors in the country.

The next day, the Orlen venture said it has no plans to cooperate with Bedzin and that the power producer had asked it to sign the NDA. Premier Morawiecki weighed in, saying on Twitter that he had asked the regulator for a report that would allow the authorities to “take the next steps.”

The utility tumbled 55% on Thursday — the biggest decline on record — to 32 zloty per share, compared with 6.75 zloty on May 31. The Polish regulator said it was undertaking a “thorough analysis” of the situation, vowing to inform the authorities if it finds “justified suspicion of the use of confidential information or manipulation.”

Bedzin, whose market value has swollen to 101 million zloty ($25 million), said in a statement that it has “made every effort to inform the market about matters important to the company.” The firm didn’t reply to Bloomberg requests for further comment.

Orlen and its partner Synthos, owned by billionaire Michal Solowow, plan to invest $4 billion in small nuclear reactors based on GE Hitachi’s technology. The project is seen as key for country’s energy transformation away from coal.

Before this month’s rally, Bedzin had for months struggled with rising costs of carbon allowances needed to run its coal-powered heating and power plant in southern Poland.

(Updates with closing share price in paragraph 4.)