DALIAN, China — Three undercover investigators who were seeking evidence of abusive labor practices in the manufacture of Ivanka Trump-branded shoes have been released on bail from a detention center in southeastern China pending a trial, the activist group that employed the investigators said on Wednesday.

Their release on bail represents the first confirmation that the three men have been thrust into China’s labyrinthine criminal justice system, and have not just been quietly detained for a few days. China Labor Watch, the group that sent the men into two factories that produce Ivanka Trump shoes, called for them to receive a fair trial.

The spokesman for the public security office in Ganzhou, where the men had been held, did not respond to telephone calls requesting comment.

The Ivanka Trump brand declined to comment on their release on bail, and Ms. Trump has not commented on the investigators’ detention. She has been publicly urged to do so by the best-known Western expert on China’s criminal justice system, Jerome Cohen, a professor at New York University who has specialized in the subject for a half-century. Mr. Cohen has said that public comments from her would considerably help the legal prospects for the men and the conditions under which they were held.