A UN body tasked with cutting global aircraft emissions is covertly meeting this week for discussions dominated by airline industry observers.

The environment committee of the International Civil Aviation Organisation (ICAO) meets on Monday in Montreal behind closed doors to discuss measures to reduce emissions from international aircraft. Domestic and international flights emitted 895m tonnes of CO2 last year – 2.4% of global energy-related CO2 emissions, according to Carbon Brief. In terms of emissions, if aviation were a country it would be the sixth largest in the world.

But the body in charge of reducing the carbon footprint of international aviation has little or no public scrutiny. Its agenda and discussion documents are not released to the public or the international press, and the meetings are not open to the media.

Anyone who leaks documents being discussed faces “unlimited liability for confidentiality breaches”, according to ICAO rules.

Key observers at Monday’s meeting of the committee on aviation and environmental protection (CAEP) are a number of industry bodies. They include the International Business Aviation Council, the International Federation of Air Line Pilots’ Associations, the Arab Civil Aviation Commission, the International Coordinating Council of Aerospace Industries Associations, the Airports Council International and the International Air Transport Association. The only non-governmental body not linked to the airline industry allowed into the meeting is the International Coalition for Sustainable Aviation, made up of a small group of international environmental NGOs.

Nadja Kostka, climate project coordinator at Transparency International, said: “Agencies which set common global standards for large, international industries have to be transparent in order to prevent capture by corporate interests, or even the appearance of undue influence.

“The ICAO currently meets behind closed doors, including for discussion about emissions, which affect the entire planet. We’ve seen similar situations at other UN agencies … we strongly believe that all UN bodies need to commit to transparent ways of working in order to gain the public’s trust.”

The key discussions on reducing emissions come amid growing pressure from some countries – and their airlines – to open the doors to all types of biofuels, including those which cause environmental destruction, such as palm oil-based fuels.

Indonesia, one of the largest palm oil producers in the world, is one of 24 member states whose representatives will be deciding in secret to recommend whether future new airline fuels have to be sustainable.

Malaysia, which is not a member of CAEP, is pushing a campaign – Love my Palm Oil – to extend it to non-food use, supported by its three main airlines.

Twenty-four countries, including the UK, France, Canada, Singapore, Russia and the US, have representatives at this week’s meeting.

This year international aircraft will for the first time have to start monitoring their emissions as part of ICAO measures to reduce emissions with a market-based system of purchasing emissions offsets – rather than by directly reducing aircraft emissions.

They can reduce the amount of carbon emissions they have to offset by using biofuels, but as yet there has been no agreement by member countries on restricting the new fuels to those which are sustainable.

The scheme was agreed in 2016 by the ICAO countries. But few believe it will have the required impact on cutting emissions in a growing aviation industry in which passenger numbers are predicted to double to 8.2 billion in 2037.

The International Council on Clean Transportation (ICCT) said it could only be expected to “modestly reduce” the net climate impact of international aviation up to 2035.

Andrew Murphy of the NGO Transport and Environment, said the lack of transparency gave little confidence that the ICAO would tackle emissions, adding: “Media are free, and in fact encouraged, to cover similar meetings in other UN agencies …

“It’s well past time that ICAO brought its media practices into line with the rest of the UN family, a move which would help raise confidence in its decision-making.”

Last year Saudi Arabia – with the backing of the US – secured a new definition at the ICAO of alternative fuels to include “clean oil” because the refinery producing the oil was run on renewable electricity – something Murphy said amounted to “greenwash oil” and was “an awful deal for the climate”.

The environmental NGOs are calling for the ICAO and all its committees to open to the public and remove threats of “unlimited liability” for members who release documents.

“At present, state and observer submissions to CAEP remain unavailable to those outside of CAEP,” they said.

“When such submissions contain commercially sensitive information, such secrecy may be acceptable. However, this justification oftentimes deserves to be challenged, as information from manufacturers which is submitted to CAEP is, as a matter of course, available to other manufactures, and therefore no harm can be identified from making it available to a broader range of actors.

“Such a level of secrecy stands in contrast to other UN agencies.”

Under the Paris climate change agreement, emissions from international aviation are not specifically included in national climate targets required by countries to pursue efforts to limit global temperature increases to 1.5C. This leaves ICAO as the primary body for reducing airline emissions.

A spokesman for ICAO provided the Guardian with a list of attendees to the meeting and said the meeting results would be made available, but not the discussion papers. “Only the CAEP members and recognized observers are permitted in the room for said discussions,” he said.