Members have also spoken of their unhappiness at the proposal, accusing the ILM board of trying to rush it through.
The two organisations announced last month that the ILM, which supports legacy professionals and has about 300 charity members and more than 500 individual members, was consulting members on a proposal for it to become part of the IoF.
Under the plan, which has the backing of both boards, the ILM would be dissolved as a company and its three members of staff would join the IoF, which employs 40 people.
The ILM would become a special interest group of the IoF – the SIGs collectively elect one person to join the IoF board. The initiative could be completed as soon as this summer.
The proposal will be discussed at the ILM’s annual conference on Friday.
On Monday, members were asked to complete a short survey by 5pm on Tuesday afternoon, indicating whether they would say "yes", "no" or "undecided" if they were asked to vote on the proposed merger at that moment.
As of yesterday’s deadline, 198 members had completed the survey, with 50.5 per cent saying they were against the proposal, 33.3 per cent in favour and 16.2 per cent undecided.
The results will be discussed at the conference but, speaking before the meeting, some members said they were unhappy at the proposal and that the board had treated them with contempt.
One member, who asked not to be named, said: "We are being asked, effectively, to endorse a major change negotiated not just without any mandate from the members – ie you – but also in secret.
"I remain open to persuasion, of course, but I do not yet see any evidence or argument to support this abandonment of our interests. In my view, the proposed merger does not deserve serious consideration."
Another ILM member, who asked to remain anoymous, complained about a "hastily arranged" question-and-answer session, organised by the board last week, which the member said was badly attended.
"I share the disquiet over this proposed merger and the apparent speed and secrecy with which it has been arranged," the member said. "I see no advantage in losing our independence. You may have seen notes of the meeting on 8 May, arranged at too short a notice to get many attendees, another point of concern indicating what I saw as a rather contemptuous approach to the members’ views."
The ILM said the survey was an informal poll rather than a binding vote and that members would be asked to vote formally on the proposal at an extraordinary general meeting, the date for which has not yet been set.
Simon West, chief executive of the ILM, said members would have the last word on whether the proposed merger should go ahead and denied it had acted without a mandate from members.
"The board has the authority to act in the best interests of the organisation," he said. "We are now in the process of consulting members to see if there is agreement on this proposal. The board is still in favour of these proposals, but members have the ultimate say."
The IoF said the decision was in the hands of ILM members. Peter Lewis, chief executive of the IoF, said: "The ILM is consulting its membership on its proposals to merge with the IoF. If approved by ILM members, they would become members of the IoF and take advantage of all the benefits of individual IoF membership, while maintaining their brand identity and the training and support they currently receive through the ILM."