Only 29 out of 72 recently contacted companies are releasing information about how they source their products in Bangladesh, and "many brands have held out completely," New York-based Human Rights Watch said in a report.
That makes it impossible to hold them accountable for ensuring safe conditions at factories they work with, the group said.
Bangladesh's garment industry has invested more than $1bn in safety improvements since April 24, 2013, when the Rana Plaza garment factory complex collapsed outside Dhaka, killing more than 1,130 workers and injuring 2,500.
The collapse highlighted grim conditions in the country's garment industry, the second largest in the world with about 4,000 factories employing about 4 million workers and earning $25bn a year from exports, mainly to the United States and Europe.
Enjoy curated articles directly to your inbox.