Activist investor Legion Partners Asset Management has criticized the planned sale of SurveyMonkey parent Momentive Global to software services company Zendesk and said it would do “whatever is necessary” to block the deal, according to Bloomberg.

Last week, Zendesk announced that it would pay 0.225 shares of its own stock for each Momentive share, which worked out to a price of $28 per share, about $4 billion. However, a plunge in the market capitalization of both companies, especially that of Zendesk, has taken the offer to a value of just $22.80 per share as of Friday’s close.

Legion, a 1.4% shareholder in Momentive, said in a Monday emailed statement to Bloomberg that it has concerns about the value of the transaction and the process that led to it.

“Legion Partners is strongly against the proposed acquisition of Momentive by Zendesk and is willing do to whatever is necessary to put an end to this deal,” the activist said, adding that it believed Momentive’s board is in need of a “significant upgrade.”

Another activist investor raised similar concerns. Cannell Capital junior portfolio manager Oleg Karmanov said in an interview that the market reaction to the deal suggests that Momentive either didn’t negotiate hard enough to obtain the best possible offer or didn’t sufficiently gauge takeover interest.

A spokesperson for Momentive rejected the assertion. “The Momentive board undertook a robust and comprehensive review with a process designed to enhance shareholder value and determined that the transaction with Zendesk was the best outcome for Momentive shareholders,” the spokesperson said in a statement to Insightia. “We are committed to closely engaging with our shareholders to ensure they recognize the significant value inherent in the combination.”

In September, Legion sent a letter to Momentive’s top echelon complaining about their inability to lift the stock price and calling for an auction. The activist noted that Momentive’s stock lagged a leading technology ETF by a wide margin and blamed the “board’s poor governance, oversight, and inability to take strategic action to drive stockholder value” for the underperformance.

“We are increasingly disappointed with Momentive’s board of directors and their continued disregard toward shareholders, as well as their own fiduciary duties,” Legion told Bloomberg on Monday. “Given these recent developments, we believe changes that will significantly upgrade Momentive’s board have never been more urgently needed.”

Shares in Momentive were unchanged at $22.92 each as of 10:40 a.m. EDT Monday while those of Zendesk were down 1.3% at $100.50 each.

The Momentive-Zendesk transaction is expected to be put before shareholders of both companies.