As UN diplomats convened in Bonn, developing nations were baulking at the latest draft of a global climate agreement to be inked in Paris in December, negotiators and experts said.
The five-day session is the last formal parlay before heads of states and ministers gather in the French capital to seal a deal to beat back the threat of global warming and help poor nations cope with its impacts.
Monday (local time) will be the first opportunity for rank-and-file negotiators to weigh in on a new draft by two senior diplomats from Algeria and the United States.
Reactions from developing nations and veteran analysts of the talks, now in their third decade, suggest that sparks will fly at the opening session.
Many countries are likely to insist that deleted passages be restored before the arduous job of line-by-line revisions can even begin.
"The text... cannot be used as a basis for negotiation, as it is unbalanced," the African Group said in a statement released hours before the opening session.
The new draft "does not reflect the African Group positions, and crosses the group's red lines," it said.
The African nations' viewpoint is shared by other blocs under the more than 100-strong "G77 plus China" umbrella.
"There is no question that this new text will definitely anger some parties, or all parties in some ways," said Jens Mattias Clausen, a climate change adviser for Greenpeace.
One make-or-break issue is finance.
Rich nations have pledged to mobilise US$100 billion per year from 2020 to help vulnerable countries reduce their greenhouse gas emissions and cope with the impacts of global warming.
Developing nations want firm commitments, not just on the total amount but also where it will come from and what it will be used for.
Another key element that many countries say was sidelined is a timetable for reviewing and ramping up national commitments – submitted ahead of the November 30-December 11 conference – to slash carbon emissions.
The pledges are a key pillar of the agreement, which would take effect in 2020.
Rich countries have acknowledged their historical responsibility for global warming, but insist that rapidly growing economies, among the biggest emitters, need to take on more of the burden.