Hohn, who runs hedge fund TCI Fund Management, owns 3.1% of Cellnex's shares and 5.9% in derivatives, corporate records show.

Spanish companies have largely avoided the attention of activist investors. However, Hohn last month wrote to Airbus, in which TCI has a 3% stake, demanding it drop a deal.

Cellnex declined to comment.

"We believe that the subsequent hiring process for a new CEO has been mishandled by the board and resulted in insufficient progress to recruiting a suitable replacement," Hohn wrote in the letter, published on TCI's website.

"Cellnex is a great company, but in our opinion it cannot reach its full potential because it is held back by poor corporate governance."

The Barcelona-based group announced in January that its chief executive Tobias Martinez would step down in June after it embarked on a strategy shift away from acquisitions to focus on lowering debt.

It also said Martinez would attend the shareholders' Annual General Meeting (AGM) scheduled for June 1.

"We intend to exercise our shareholder rights to request certain shareholder resolutions be added to the next AGM," the letter said.

"We currently intend to propose resolutions at the AGM removing Bertrand Kan (Chairman), Peter Shore and Alexandra Reich as directors and appoint Jonathan Amouyal (of TCI) as a director and potentially additional directors."

Kan was named Cellnex's chairman in 2015 and is an independent member. Shore, also independent, was named board member the same year; while Reich was named in 2020 representing Singaporean sovereign wealth fund GIC Private Limited, which holds a 7% stake in Cellnex, and is part of the nominations committee, according to records.

The letter was first reported by the Financial Times.

(Reporting by Joan Faus and Andres Gonzalez; editing by Barbara Lewis)

By Joan Faus and Andres Gonzalez