By Svea Herbst-Bayliss

BOSTON (Reuters) -Proxy advisory firms Institutional Shareholder Services and Glass, Lewis & Co on Friday told investors in Zendesk (NYSE:) to vote against a planned takeover of Momentive Global, the parent of web-based survey portal SurveyMonkey, arguing the deal is too risky.

Glass Lewis and ISS both voted no to the agreement after a large number of shareholders were also against it. This means that there are less chance than ever that software company shareholders will approve the deal when they vote this month.

“We believe Zendesk’s proposed acquisition of Momentive could readily be characterized as a case of, ‘ready, fire, aim’,” Glass Lewis analysts wrote in a note, adding, “we recommend shareholders vote AGAINST this proposal.”

ISS said that support for the proposal was not warranted and noted the many uncertainties surrounding revenue synergies, financial projections, and that this “had potential to become the rarest of particular situations,” a merger that shareholders both of the seller and buyer dislike.

Zendesk purchased Momentive for $4 billion in an all cash deal in October. Investors including Jana Partners an activist hedge fund, quickly criticized the deal, pointing out its logic and financial merit.

Glass Lewis agreed and wrote: “We do not believe Zendesk investors — perhaps seeking some stability in the wake of the Company’s seesawing quarterly performance — have been afforded persuasive reason to conclude the Company is well positioned to efficiently realize the lofty objectives underpinning the Momentive transaction.”

Zendesk announced that it has received takeover interest but rejected an offer of $127-$132 per share from several private equity firms. Zendesk wanted to continue with its plans to purchase Momentive.