Activist investor White Tale has boosted its stake in Clariant to 15.1% from 5.13% in early July as it continues to try and scupper the proposed $20 billion merger with Huntsman. In an open letter dated Sept. 19 to Clariant’s board of directors, the US investor, which comprises hedge funds Corvex and 50 North, reiterated its view that the deal would destroy shareholder value.

White Tale, which is Clariant’s largest shareholder, stated: “As you know, we have attempted to work constructively with you and your advisors over the past two months, out of the public spotlight, to better understand the board’s questionable logic in pursuing Clariant’s proposed merger with Huntsman. Unfortunately, we remain convinced, and increasingly so, that the proposed merger is detrimental to Clariant shareholders.”

The investor claimed the deal would reverse the Swiss group’s strategy of transforming into a pure-play specialty chemicals company, returning it to an “unfocused and commodity-oriented business with increased volatility and a lower market multiple.” It also alleged that Clariant’s board had not “seriously explored alternative measures or transactions to maximize shareholder value in advance of agreeing to merge with Huntsman.”

In a scathing attack on White Tale, Huntsman CEO, Peter Huntsman, said the investor had “advanced a destructive, high-risk strategy of dismantling Clariant and denying all other stakeholders of the company the sustainable, long-term benefits of this compelling combination.” Huntsman added that he had not met with White Tale and had no intention to do so.

Clariant repeated its conviction that the merger was the “perfect transaction at the right time to create substantial immediate and long-term shareholder value.” However, it needs two-thirds of its shareholders to approve the deal at a meeting expected to take place in November. The company’s management is said to be doing everything possible to boost attendance at the meeting, aware that a low turn-out could jeopardize the merger and play straight into White Tale’s hands.