DONGGUAN, China — The Chinese factory workers who make shoes for Ivanka Trump and other designers gather at 7:40 every morning to sing songs.

Sometimes, they extol worker solidarity. Usually, they trumpet ties between China and Africa, the theme of their employer’s corporate anthem.

That’s no accident. With many workers here complaining about excessive hours and seeking higher pay, the factory owner wants to send their jobs to Ethiopia.

The employer, Huajian International, now faces scrutiny from labor activists for how it treats workers. Chinese authorities this week detained an activist who went undercover in the company’s factory here for a labor rights group. Two other activists who worked at Huajian are missing; it’s unclear whether they were detained.