The Boston Celtics center, who has been outspoken about the treatment of minorities in China, wore customized shoes in his team's win against the Charlotte Hornets on Monday with the words "Modern Day Slavery" and "No More Excuses" written on them.
On Monday, he posted a video on Twitter in which he called out Nike for its silence on injustice in China.
"Nike remains vocal about injustice here in America, but when it comes to China, Nike remains silent," said Kanter, in a post which used the hashtags #HypocriteNike and #EndUyghurForcedLabor.
"You do not address police brutality in China, you do not speak about discrimination against the LGBTQ community, you do not say a word about the oppression of minorities in China, you are scared to speak up."
Kanter's criticism centered particularly on the injustice felt by the Uyghur community -- the US State Department estimates that up to 2 million Uyghurs and other ethnic minorities have been detained in internment camps in Xinjiang since 2017.
In a three-hour interview with CNN, conducted in Europe where he is now in exile, an ex-detective turned whistleblower revealed rare details on what he described as a systematic campaign of torture against ethnic Uyghurs in the region's detention camp system.
China has repeatedly denied allegations of human rights abuses, saying the centers are necessary to prevent religious extremism and terrorism.
"Who makes your shoes in China? Do you even know?" Kanter added, the footwear industry was "tainted" by the enforced labor.
"There are so many forced labor factories in China. For instance, Uyghur forced labor, it is modern day slavery, and it is happening right now in China.
"Millions of Uyghurs are currently detained, sold and assigned to work at forced labor camps, prisons and factories across the country. They are under constant surveillance, with long working hours and poor living conditions.
"Don't forget, every time you put those shoes on your feet, or you put that T-shirt on your back, there are so many tears and so much oppression and so much blood behind it all."
Earlier this year, Nike released a statement saying it did not source products from the Xinjiang region.
"Nike is committed to ethical and responsible manufacturing and we uphold international labor standards," said the statement.
"We are concerned about reports of forced labor in, and connected to, the Xinjiang Uyghur Autonomous Region (XUAR).
"Nike does not source products from the XUAR and we have confirmed with our contract suppliers that they are not using textiles or spun yarn from the region."
Nike was not immediately available for comment about Kanter's latest video when asked by CNN.
Kanter ended the video by inviting Nike's co-founder Phil Knight and high-profile ambassadors LeBron James and Michael Jordan to a trip to China so they can "see [it] with your own eyes" where the shoes are made.
"Nike likes to say 'Just Do It' -- well, what are you doing about the slave labor that makes your shoes? That slave labor that makes you rich," he added.
"Nike must be a participant in this. Stop the hypocrisy, stop the modern-day slavery now."
Last week, Kanter criticized China's treatment of Tibet which led to Chinese Foreign Ministry spokesman Wang Wenbin telling a news briefing that the NBA player was "trying to get attention" and that his remarks "were not worth refuting."
The broadcast of the Celtics' season-opening game against the New York Knicks was pulled by Chinese video-streaming site Tencent as a result, while fans took to Chinese social media to denounce Kanter and the Celtics.
It comes two years after Daryl Morey, the then-general manager of the Houston Rockets, sparked controversy between the NBA and China with a tweet -- subsequently deleted -- in support of pro-democracy protestors in Hong Kong. Morey stepped down a year later.
Kanter, who was raised in Turkey, has been vocal before in defense of various political causes, including criticisms of Turkish President Recep Tayyip Erdogan.
He faced death threats and the criminal trial of his father back home as a result.