More than 400 people were killed in the April 24 collapse of the Rana Plaza building outside Dhaka; the building housed several garment factories that made products for Western brands.
News reports say that workers at the factories housed in the building were paid about 38 euros a month (about $50).
"This was the payment of these people who have died," the pope said, according to Vatican Radio. "And this is called 'slave labor!' "
Francis' comments came at a Mass Wednesday to mark the feast of St. Joseph the Worker.
"Not paying a just [wage], not providing work, focusing exclusively on the balance books, on financial statements, only looking at making personal profit. That goes against God!" the pope added, according to Vatican Radio.
As NPR's Jim Zarroli reported in March, Francis' "writings and public comments make clear his sympathies lie with the world's desperate and destitute. In the process, he has sometimes cast a suspicious eye on the institutions of capitalism, once branding the International Monetary Fund's debt policies 'immoral.' "
The pope's comments follow a meeting between major retailers and labor activists in Germany this week to work out a deal on improving working conditions in Bangladesh, where the garment sector is a $20 billion industry. NPR's Steve Henn reports on All Things Considered:
"At the meeting, activists pushed retailers who use factories in Bangladesh to start spending their own money to make those workplaces safer.
"The proposed deal would have an enforceable arbitration clause, would require the use of highly qualified fire and safety inspectors — and require those inspection reports to be made public. It would also mandate that the Western brands pay for any needed repairs. Workers would also have the right to refuse to enter buildings they believe are unsafe."
But as Steve notes in that story, some of the larger retailers such as Wal-Mart are still far away from making such commitments ahead of a May 15 deadline for a deal. (In a separate story for NPR's Morning Edition, Steve traces the social auditing industry, which began as a way to monitor the child sweatshop scandals of the 1990s.)
Improved working conditions in countries such as Bangladesh would likely mean higher price tags on many of the products we buy. How much more consumers are willing to pay for products made in places with fair working conditions is the subject of academic research, as NPR's Dan Bobkoff reported:
"Ian Robinson of the University of Michigan and his team ran an experiment at a suburban Detroit department store. They placed identical socks side by side on display. Some were labeled as coming from factories with good working conditions. Half of the customers noticed the choice and bought them. When the researchers started to raise the prices on the ethical socks, however, there were fewer takers.
" 'As soon as we introduced a small price difference, just 5 percent different, it dropped down to about 33 percent,' Robinson says.
"When prices were 20 percent or as much as 50 percent more than the regular socks, about a quarter of shoppers chose to pay more, 'at least in part motivated by ethical concerns,' he says."
Also Wednesday, hundreds of people attended a mass funeral for dozens of garment workers whose bodies could not be identified.