zCapital, which owns a 0.7% stake in Baloise, wants to abolish a 2% ceiling on voting rights, arguing it would make the insurer more attractive to investors.

The proposed reform is the latest attempt to overhaul corporate governance at Swiss companies that are often protected from shareholder pressure by complex share structures, voting rules and large family holdings.

Proxy advisors ISS and Glass Lewis have backed zCapital's initiative, which will be put to shareholders at Baloise's AGM on April 26. The asset manager said Swiss proxy advisors Ethos and Inrate had also backed its proposal.

"We want a one share, one vote regime which is fairer for all the shareholders," zCapital CEO Hilmar Langensand told Reuters. "The current restrictions are a relic of the past."

Shareholders currently have no more than 2% of votes, irrespective of the size of their stake, meaning that major investors like BlackRock or UBS cannot fully bring their weight to bear on decision-making.

Langensand said abolishing the restriction would create a "healthy balance" between shareholders and the board. zCapital describes itself as a long-term investor in Baloise, having held a stake since 2008.

Baloise has recommended rejecting the proposal, arguing that lifting the curbs was in the long-term interests of neither the company nor most shareholders.

In a statement, Baloise said a proposal should be drawn up for the 2025 AGM that best takes into account the interests of the company, shareholders and other important stakeholders.

For zCapital's motion to pass, it needs support from 75% of shareholders represented at the AGM. "We have four proxy advisors supporting our request, and we are confident we will get a good result," Langensand said

(Reporting by John Revill, editing by Dave Graham)