Southeastern Asset Management (SAM) investment fund working with Egyptian billionaire Nassef Sawiris said on Wednesday it has snapped up a 3 percent stake in Sika.
SAM backs the Swiss chemicals and construction group's battle against a takeover by France's Saint-Gobain, the U.S. based company said in a statement.
It also told Les Echos newspaper it intended to act as a mediator in the dispute.
Sawiris is also French cement maker Lafarge's second bigger shareholder with a 16 percent holding.
In December, the SWH holding of the Burkard-Schenker family, which controls Sika with a 16.1 percent stake and 52.4 percent of voting rights, agreed to sell control of the chemicals company to Saint-Gobain for 2.75 billion Swiss francs ($2.95 billion).
But Sika management and several shareholders have been opposing the transaction, triggering a legal and administrative battle.
They argue that Saint-Gobain should not be allowed to get control of the company without making a full blown bid.
The Burkard-Schenker family's holding company had its Sika voting rights clipped at 5 percent during an April 15 shareholder meeting, blocking the Saint-Gobain transaction.
"Southeastern believes the sale of the family's 16 percent stake to Saint-Gobain at an 80% premium without a competing offer to other shareholders disadvantages all non-family Sika stakeholders - its employees, customers, and in particular, other owners - and should not proceed as currently structured," SAM said in a statement.
Sika confirmed its outlook on Wednesday at an investor day as it held an extraordinary general meeting to vote on the removal from office of several board members and the election of a new chairman.
"In its role as an engaged owner and constructive long-term shareholder, Southeastern will seek to work with all relevant parties to explore strategic scenarios that deliver full and fair value for the benefit of Sika stakeholders," SAM said in its statement.
Sika shares were down 0.57 percent by 0854 GMT while Saint-Gobain shares were flat.
