Sinclair made the comment in response to a tweet from Dezeen that quoted an article about unpaid internships in Japan.
The article, published in April, explored the Japanese "open desk" culture that sees young architects gain work experience in studios, often working long hours for no pay.
In the article, LABtokyo founder Nicholas Raistrick stated: "Voluntary work here is really quite common and people do make sacrifices without expecting immediate reward."
Intern culture "rewards wealthy, privileged designers"
Sinclair replied: "'Voluntary work' is radically different than unpaid internships (aka digital slavery)," he tweeted.
Sinclair made the comment in response to a Dezeen tweet about an article where designers defended the culture of unpaid internships in Japan.
In response to this comment, Sinclair said that he had first-hand knowledge of many young designers that had been taken advantage of in Japan.
"This culture rewards wealthy, privileged designers and pushes out those with economic or social challenges," his tweet continued. "I've met many young designers in Japan and they are used and abused by firms."
Architects "exploit young professionals"
In a subsequent tweet, Sinclair added that the use of unpaid interns in major cities like London, New York and Los Angeles benefits designers who come from wealthy families.
"High profile architects knowing [sic] exploit young professionals and perpetuate class division and elitism by encouraging unpaid internships in their practice," he tweeted.
"Meaning designers from wealthy families can afford for live in London/NY/LA w no salary."
The controversy over unpaid roles in architecture hit the news earlier this year when it was revealed that Junya Ishigami, the Japanase architect of the 2019 Serpentine pavilion, used unpaid internships.
The following row about the use of unpaid labour in architecture led to several architecture studios ended their unpaid internship programs including Chilean architecture studio Elemental and Tokyo-based Sou Fujimoto Architects.
"The RIBA strongly condemns exploiting students in this way," former RIBA president Ben Derbyshire told Dezeen at the time. "This exploitation of talent runs counter to a diverse and inclusive profession and must be stamped out."
Japanese studios offer unpaid positions
However many small Japanese studios continue to offer unpaid open-desk positions to interns.
Raistrick, who's LABtoyko training consultancy works with architects and designers, said the practice was part of Japanese culture of masters and apprentices.
"It is a strong part of the social fabric and something that helps keep Japan running so smoothly," said Nicholas Raistrick
"It's not a job, it's a life-changing experience," one Japanese architect told Dezeen. "It has a profound impact on their career."
Architect Sou Fujimoto openly discussed the issue in an interview with Dezeen in 2013. "In Japan we have a long history of interns and usually the students work for free for several periods," he said at the time.
"It's a nice opportunity" for both employer and intern," he said. The employer gets to know the younger generations, who in turn learn "how architects in Japan or different countries are working".
New York designer Karim Rashid also defended the use of unpaid interns earlier this year.
"I believe some of the universities are far more exploiting than a small brilliant architecture firm that can inspire and be a catalyst for a student's budding career," Rashid said in April.
The designer argued that unpaid work in a studio was less exploitative than paying for an expensive education.
"I believe some of the universities are far more exploiting than a small brilliant architecture firm that can inspire and be a catalyst for a student's budding career," he said.
Sinclair is a pioneer of socially responsive architecture who is currently executive director of Armory of Harmony – an organisation that makes musical instruments from decommissioned weapons.
He co-founded Architecture for Humanity in 1999 as a charity that aimed to create architectural solutions to humanitarian crisis around the world. He has worked in Kosovo, Afghanistan and Haiti and led the organisation's efforts in Japan to rebuild after the tsunami in 2011.
After leaving Architecture for Humanity, Sinclair worked at Brad Pitt and Angelina Jolie's humanitarian charity the Jolie-Pitt Foundation, before heading up Airbnb's humanitarian programme. In recent years he has also collaborated on several preservation projects in rural Japan.