General Electric Co. Chief Executive John Flannery sent a stern warning to those eager to bet on further share declines in the embattled conglomerate, saying bearish investors do so “at their own peril.”

Investors may be listening. GE shares GE, -2.41% had tumbled as much as 3.7% early Monday, touching the lowest level since July 6, 2010, before bouncing back to a gain of 1.1%.

In a letter addressed to investors, customers, partners and employees, as GE released its 2017 annual report, Flannery acknowledged that a “very tough year” has left many employees “disappointed and frustrated.” The stock plunged 45% in 2017, the worst yearly performance since the 2007-09 recession, while the Dow Jones Industrial Average DJIA, -0.87% climbed 25%.

“Many people have lost faith in us. I have not,” Flannery wrote. “I want to be very clear on one thing: While I am not proud of our performance, I am incredibly proud of this company.”

Flannery’s letter comes as he has promised to be more transparent about the company’s plans, with employees and investors. After taking over as CEO on Aug. 1, 2017, he unveiled in November a transformation plan that included cutting the dividend in half and a downbeat profit outlook, but stopped short of a radical restructuring.

Then in January, GE disclosed a $6.2 billion charge and a $3 billion capital contribution to its insurance subsidiary business that will grow to $15 billion by 2024. At that time, Flannery said he was one of the “deeply disappointed” employees.

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The chief executive said on one level, he understands many employees are frustrated. But on another, he recognizes their competitive drive to win in the marketplace and to fight for the company’s reputation. “People who bet against that do so at their own peril,” he wrote.

Earlier Monday, the stock initially fell after GE said in its annual report that 2016 and 2017 earnings a share would be “restated” lower as it adopted new accounting standards, and included mention of a previously disclosed Securities and Exchange Commission investigation.

But as MarketWatch transparency reporter Francine McKenna explained, GE’s “recasting” of prior period numbers wasn’t a result of an error or misstatement, but just the company’s way of providing more disclosure and more detail about the impact of the new standards.

And to ensure the company remains transparent to all, GE said it was nominating a former chairman of the Financial Accounting Standards Board, Leslie Seidman, to its board of directors.

“Some of the people who follow the company closely, like media and analysts, examine the past and demand accountability,” Flannery wrote. “I understand this.”