The CFO of renewable energy company Innogy was attacked on his way home from a bakery. The company's parent, RWE, has been confronting protestors over its open-pit coal mines.

Bernhard Günther sustained serious injuries.

An acid attack on an executive of energy firm Innogy has escalated security fears for senior businessmen in normally peaceful Germany and revived painful memories of the terrorist attacks that rocked corporate Germany three decades ago.

Bernhard Günther, the chief financial officer of Innogy, was on his way home from a bakery in suburban Haan, outside Düsseldorf, Sunday morning when two men attacked him in a park, pouring acid over his head. While the two attackers fled, Mr. Günther, 51, managed to make his way home and called authorities.

He was evacuated by medical helicopter and is now being treated in a specialty burn clinic for his wounds, which are not life-threatening but have left him in serious condition.

We are all dismayed and horrified by this terrible act. Rolf Martin Schmitz, CEO, RWE

Police said they had no apparent motive for the attack. Innogy is the renewable energy subsidiary of electric utility RWE, which has been engaged in a long-running battle with environmentalists over its open-pit coal mining in the country. Protesters have set up encampments in the Hambach Forest near Cologne to protest the company's coal mining.

“We are all dismayed and horrified by this terrible act,” said RWE CEO Rolf Martin Schmitz. The firm’s competitors joined in expressing outrage at the assault. “The attack left me stunned,” said Johannes Teyssen, CEO of rival electric utility Eon.

While German firms are normally very reticent to discuss corporate security, a number of companies in the energy sector said privately that they had stepped up security for their executives as a precaution on Sunday.

As recently as last December, police in Potsdam outside Berlin evacuated a Christmas market after a bomb was found there. It was later determined to be part of a plot to extort money from the package delivery service DHL, which is owned by Germany’s privatized post office.

But in the dark days of the Red Army Faction, also known as the Baader-Meinhof gang, terrorists killed Alfred Herrhausen, the chairman of Deutsche Bank, the country’s largest financial institution, with a roadside bomb that destroyed his armored Mercedes-Benz limousine in November 1989.

The RAF also killed a Siemens executive and wounded several other German businessmen. After the fall of the Berlin Wall, it was discovered that the East German secret police known as the Stasi had been funding the RAF and providing logistical support. The group later announced that it was disbanding.

Since the end of the RAF, there have only been a few incidents involving Gerrman corporate executives. Most senior managers get company protection when traveling abroad, especially to high-risk countries like Mexico, but shun security at home in Germany.

Innogy has been in disarray in recent months following the departure of its Dutch CEO Peter Terium a few days after the company issued a profit warning at the beginning of December. The company’s supervisory board said it did not have faith in Mr. Terium’s plan to turn the company around.

Mr. Terium spent lavishly on management consultants and digital innovations. The supervisory board is now demanding that the company adopt measures to reduce its expenses.

Since Mr. Terium’s departure, Innogy has been managed by its former human resources chief, Uwe Tiggs. Now with Mr. Günther incapacitated for several months, the company’s outlook is even more clouded.

Peter Brors, Jürgen Flauger, Axel Höpner, Sönke Iwersen, Christoph Kapalschinski, Jan Keuchel, Kirsten Ludowig, Christoph Schlautmann and Martin Wocher contributed to this article. It was adapted into English by Charles Wallace, an editor with Handelsblatt Global in New York. To contact the authors: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] and [email protected].