The two companies agreed not to extend the contract when it runs out at the end of December, Edelman said in a statement on Wednesday.

Edelman has been working with TransCanada on the communications strategy for the proposed C$12 billion ($10.7 billion) Energy East pipeline, which would carry Alberta oil to refineries and export terminals in Eastern Canada.

Greenpeace earlier this month made public five documents on Edelman's proposal for TransCanada to take direct aim at its critics and go after supporters for the pipeline. The environmental group said the tactics were like those used by U.S. oil companies.

One document says Canadians need "a true picture of the motivations" of opponents and recommends recruiting third parties to "put the pressure on, especially when TransCanada can't."

Greenpeace said the documents showed TransCanada was using "deceitful tactics."

TransCanada spokesman James Millar said that the documents contained draft strategy recommendations, many of which were never implemented.

Edelman said on Wednesday its strategy was "ethical and moral," but that given the vocal criticism, it was best for TransCanada to find a new partner.

Calgary-based TransCanada is also developing the stalled Keystone XL pipeline, which would carry Alberta crude across the border into the United States to Gulf Coast refineries.

Environmental and other activists in North America are fighting the construction of new pipelines, which they believe will foster the expansion of the landlocked oil sands and hasten the negative effects of climate change.

TransCanada filed for regulatory approval of the 1.1-million-barrel-per-day Energy East pipeline last month. The project involves converting natural gas pipelines to carry oil through to Eastern Ontario, with new pipe built through Quebec and New Brunswick.

(1 US dollar = 1.1234 Canadian dollar)

(Editing by Jeffrey Hodgson and Lisa Von Ahn)

By Julie Gordon