The Tokyo Olympic organizing committee's codes for the sustainable procurement of timber used in building venues allow contractors to use materials from questionable sources, a representative of the environmental group Rainforest Action Network said Thursday.

The Sustainable Sourcing Code for Timber provided a "huge compromise in favor of the construction companies," group senior adviser Hana Heineken told a press conference in Tokyo.

The code only requires wood used in concrete formwork to be legally harvested. It says consideration must be given to conservation of the ecosystem, indigenous and local people's rights, and appropriate safety measures, but makes none of that mandatory.

"It actually only needs to satisfy the first criteria which is legality, and if the company can satisfy the sustainability criteria, that's preferred but it is not required," Heineken said.

The stipulation means disposable wood used in formwork -- the construction of foundations -- falls under an exception, as other timber used in building facilities for the Tokyo 2020 Summer Games must meet different standards.

Heineken and Yuki Sakamoto, from the Global Environmental Forum, presented evidence to back their claim that plywood used at the National Stadium construction site is sourced from Shin Yang, a Malaysian company they claim uses questionable, and even possibly illegal, forestry practices in Sarawak, a Malaysian state in northern Borneo.

"The use of timber from Sarawak for Olympic construction, particularly from this company Shin Yang, really calls into question the standards that the Olympic committee and the Japanese government are using to ensure the timber is legal and sustainable,"

said Heineken.

The Japan Sports Council is responsible for overseeing construction of the National Stadium, and initially it was not bound by the sourcing code. But Heineken said pressure from her group led to the timber sourcing code being applied to all Tokyo 2020 Summer Games projects.

Heineken said the code is based on Japan's Act on Promoting Green Procurement, but that act is "extremely weak."

"(The law) has no due diligence requirement, and up until now...it has allowed timber from, for example, Sarawak to come into this country as legal wood," said Heineken.

Various sources including the United Nations estimate that "up to 50 percent of the timber from there is illegal," she said.

"So the standard that the Olympic committee is applying is extremely weak, and the fact that this timber was found on this construction site is a clear indicator that the standards are not sufficient to avoid the sourcing of illegal -- or timber that is of high risk of illegality -- or high risk of unsustainability."

Heineken and Sakamoto admitted that the issue is not confined to Olympic construction with almost all construction projects in Japan sourcing concrete formwork plywood from Malaysia and Indonesia due to its low cost.

But if the Olympic organizers "want to be serious about sustainability, they need to do better due diligence on their supply chains," said Heineken. "And from what we've seen, they have not been willing to do that."