BOGOTA, May 21 (Reuters) - The largest group of shareholders in Canadian oil producer Pacific Rubiales Energy Corp is "extremely disappointed" in a C$6.50-per-share takeover bid from Alfa SAB de CV and Harbour Energy Ltd, and will vote against the deal, the investors said on Thursday.
O'Hara Administration Co, speaking on behalf of the Venezuelan shareholder group which owns just under 20 percent of Pacific shares, said it was not consulted on the proposed terms of the acquisition.
"The terms agreed to by the board significantly undervalue Pacific Rubiales and are designed to deter a higher offer," O'Hara said in a statement.
Pacific Rubiales could not be immediately reached for comment.
The offer "is an opportunistic bid that does not reflect the long-term potential of Pacific Rubiales," the group said, adding that it believes shareholders would benefit from the oil company remaining independent.
The group will vote against the bid, the investors said, and is considering acquiring additional shares in Pacific Rubiales.
The company, the largest private oil producer in Colombia, said earlier on Thursday its board voted unanimously in favor of the bid from Mexican conglomerate Alfa and investment firm Harbour, but said it might consider other offers.
The bid is valued at about C$2.05 billion ($1.70 billion), or C$6.50 per share.
Pacific Rubiales had said it could accept any "superior proposal", though Alfa and Harbour would each be entitled to a $50 million termination payment if the company accepts an alternative bid.
Analysts had said the share purchases by the Venezuelan group might be an attempt to pressure Alfa and Harbour to raise their offer or a sign the investors want to launch their own bid. O'Hara says it has no plans to make an offer but could reconsider.
The news sent shares up more than 25 percent on the Toronto and Bogota stock markets earlier this month, but stabilized as the Venezuelan investors increased their ownership above Alfa's current 18.95 percent.
Besides O'Hara, the group includes IPC Investments Corp; Telmaven Overseas Inc; Volbor Trading Ltd; Memphis Investment Limited; Agency Partner Corp; Orlando Alvarado; Fundacion Nemone; and the Adar Macro Fund.
The offer comes during difficult times for Pacific, whose shares plunged 70 percent over the last year amid the fall in crude prices.
Alfa has interests in foods, auto parts, petrochemicals and telecommunications. Harbour Energy is a joint venture between Asian commodity trader Noble Group Ltd and U.S. private-equity firm EIG Global Energy Partners. (Reporting by Julia Symmes Cobb and Nelson Bocanegra,; Editing by Helen Murphy and Diane Craft)