Four activist shareholders are challenging plans to carve up DowDuPont

A quartet of well-known activist investors has lined up to pounce on plans to break up DowDuPont, the $150 billion chemicals behemoth that will be created by merging Dow Chemical Co.  and DuPont Co.  , potentially waging an unprecedented attack on the firm and Dow chief Andrew Liveris.

Jana Partners LLC and Trian Fund Management LP have privately levied concerns with how the merged company might be divided, according to people familiar with the matter, joining Glenview Capital Management and Third Point LLC, which had already voiced criticism. All four view Liveris as a roadblock to shifting certain pieces in ways they think will create value, the people said.

The swelling discontent threatens to upend his plans to close out his legacy by transforming two storied companies.

Since the merger announcement in December 2015, the plan was to combine the two firms and then splinter them into three. The investors have voiced a view that the materials company expected to emerge from the breakup -- the new version of Dow Chemical -- needs to shrink.

An attack by four activists on one company or executive would be highly unusual and would complicate the already daunting task of standing up three separate, publicly traded companies in the 18 months after the merger closes, expected in August.