Feb 28 (Reuters) - Activist hedge fund Jana Partners on Monday accused Zendesk of "hostility" toward viewpoints opposing the company, days after shareholders roundly rejected a planned deal to buy Momentive Global.

Jana Partners, which is trying to win four seats on the software firm's board, said Zendesk lead independent director Carl Bass wrote an "expletive-laden e-mail" to research firm 13D Monitor's founder Ken Squire over a note he wrote about Zendesk in early December.

The e-mail, heavily redacted to eliminate some words, was the focus of a segment broadcast on Friday by CNBC, where Squire is a contributor.

"... we have now also learned that Zendesk's board appears to condone unprofessional acts of hostility against dissenting viewpoints," Jana Partners said in a letter.

Zendesk did not immediately respond to a Reuters request for comment.

The hedge fund also reiterated that the board needs to be overhauled or "in the absence of such change, (the company) should be sold".

Earlier this month, Jana nominated four directors to the board of Zendesk, arguing that the company must be rehabilitated after an unpopular attempt to buy Momentive.

Zendesk shareholders on Friday rejected a proposed takeover of SurveyMonkey parent Momentive, shortly after Zendesk rejected a bid for itself.

The Momentive deal, valued at roughly $4 billion, was heavily criticized by prominent investors including state pension funds and large mutual funds which questioned its rationale and said it would likely be too risky.

(Reporting by Tiyashi Datta in Bengaluru and Svea Herbst-Bayliss in New York; Editing by Devika Syamnath)