Fashion brands aren't disclosing information about their supply chains, five years after Bangladesh factory disaster

Some luxury fashion brands including Dior, Chanel and Dolce & Gabbana are making public very little or no information about their supply chains and how workers are treated, according to a report out Monday.

The Fashion Transparency Index looks at whether companies provide information on tracing where garments are made, how they deal with supplier issues and who is responsible for overseeing the chain.

The luxury sector, in general, lags behind other brands and retailers when it comes to providing information about suppliers. But this is starting to change, according to Fashion Revolution, which compiled the report.

Hugo Boss, Gucci, Bottega Veneta, Saint Laurent and Burberry all score in the 31 to 40 percent range of points. Calvin Klein and Tommy Hilfiger for example, scored 37.8 percent and are the only luxury brands to disclose their tier one suppliers. Both are owned by U.S. corporation PVH. Chanel scored 3 percent, while Dolce & Gabbana scored 1.2 percent. Dior scored zero.

To compile the list, Fashion Revolution studied 150 brands that have a turnover of more than $500 million and are located in Europe, North America, South America or Asia. It rated companies based on their policy and commitments, governance, traceability, reporting and issues such as fair and equal pay and recycling. Fashion Revolution looked only at those businesses that disclose information about themselves.

Sportswear brands Adidas, Reebok and Puma topped the list, scoring 56 percent or more, meaning they have disclosed detailed supplier lists, including manufacturers, but not information such as the number of workers who are union members. Other high-profile brands that did well include H&M, Esprit, Banana Republic and Gap.

The report comes a day ahead of the fifth anniversary of the Rana Plaza factory collapse in Dhaka, Bangladesh, that killed more than 1,000 people on April 24, 2013. While progress has been made, the report states that there is still a way to go before companies are completely clear about their supply chains.

"Not enough has changed in global fashion supply chains and business practices on the whole across the industry are still very secretive," it states. "It is extremely challenging, if not almost impossible, for a consumer to find out where their clothes have been made, by whom and under what conditions.

"Never again should a tragedy like Rana Plaza happen, yet factory fires, safety accidents and faulty buildings continue to harm people in the places where our clothes are made."

If unions and workers in Bangladesh had information on where brands are manufacturing, it would be easier for them to deal with problems, according to Nazma Akter, founder of the Awaj Foundation trade union based in Bangladesh. "We don't need to do big public campaigns, we can address issues directly with brands. Having access to supplier lists also helps unions know where best to focus our organizing efforts," she wrote in the report.

Since the Rana Plaza disaster, the Bangladesh Accord on Fire and Building Safety was set up to protect workers, but it expires in May. A Transition Accord will take over, with 144 global brands signed up, covering more than 1,300 factories and around 2 million workers, according to the union IndustriALL. These brands include H&M, Zara-owner Inditex, Adidas and PVH.

Dior, Chanel and Dolce & Gabbana had not responded to CNBC's request for comment at the time of publication.