ProSieben, which operates several German television stations, had no comment. MFE had no comment on the notification, which was first reported by German media portal DE24LIVE.

Sources close to the matter said the filing was technical in nature and did not represent a new development in MFE's courting of the German company.

One of the sources said it was a necessary step under Austrian law because MFE, with its around 29.9% stake in Prosiebensat.1, could control a majority of voting rights at shareholder meetings, where turnout has been ranging between 53-56%.

The announcement, dated Dec. 13 on the Austrian regulator's website was made because ProSieben also operates in German-speaking Austria. The statement did not indicate that MFE's stake had changed in size.

MFE has long seen tie-ups among European peers as a way to respond to stiff competition in the industry from streaming groups such as Netflix or Amazon. ProSiebenSat.1 has so far shown little interest in any cooperation.

MFE, controlled by the former Italian prime minister's family, has built, partly through derivatives, a 29.9% voting stake in its German rival, cementing its position as single biggest shareholder.

The stake is just below the 30% threshold that under German law would trigger a mandatory buyout offer.

In November, MFE, struggling like its European peers with falling advertising revenues and rising costs, has called for a change in strategy at the German broadcaster, which constitutes a key part of its portfolio.

"We haven't really seen ProSieben address the big challenges the industry faces: audience decline, digital transformation ... and the need for scale to compete with digital giants," MFE finance chief Marco Giordani told analysts.

(Reporting by Michael Shields, Elvira Pollina, Klaus Lauer and Gavin Jones; Editing by Thomas Escritt, Frances Kerry and Jane Merriman)