Mr Yu said he raised these concerns with Zhu Wenjia, who ran TikTok’s algorithm, but Mr Zhu was “dismissive” and said it was “no big deal”.
Mr. Yu, who spent part of his tenure in its China offices, said he also witnessed how engineers at Douyin, the Chinese version of TikTok, tweaked the algorithm to promote content that expressed hatred of Japan. In an interview, he said that the promotion of anti-Japanese sentiment, which would make it more visible to users, was done without hesitation.
“There was no debate,” he said. “They just did it.”
The suit also accused ByteDance engineers working on Chinese apps of taking down content expressing support for the pro-democracy protests in Hong Kong while more prominently criticizing the protests.
As an example of what it described as “illegality” within the company, the suit alleges that ByteDance founder Zhang Yiming paid bribes to Lu Wei, a high-ranking government official charged with regulating the Internet. Chinese media at the time covered the trial of Lu Wei, who was indicted and later convicted of bribery in 2018, but there was no mention of who paid the bribe.
TikTok has tried to convince lawmakers that it operates away from ByteDance and that the Chinese government has no influence or special access to the app. It was working on a costly project to store American user data on servers operated in the United States by Oracle, known as Project Texas.
Mr. Yu, who was born and raised in China and now lives in San Francisco, said in an interview that during his time at the company, the data of American TikTok users was stored in the United States. But Chinese engineers had access to it, he said.
The geographic location of the servers is “irrelevant,” he said, because engineers can be a continent away but still have access. During his tenure at the company, he said, some engineers had “backdoor” access to user data.