AKS, the firm that runs the all-female idol group AKB48, announced Thursday it is “reviewing” operations of its Shanghai-based sister unit, SNH48.

According to a statement released by the group’s website, the operators of SNH48 were found to be in “contractual violations,” “necessitating a review of the unit’s operations.”

The statement did not elaborate on the trouble between AKS and SNH operators.

“Given the circumstances, we would like to inform that we have deleted all banners and other ads on SNH48 that have been carried on the AKB48 official website,” the statement read.

The firm also denied the AKB48 group’s links to BEJ48, an idol group based in Beijing, and GNZ48, one based in Guangzhou.

Yasushi Akimoto, a producer behind the AKB group, launched SNH48 in 2012 as an overseas sister group of AKB48. In August that year, two members of AKB48, Sae Miyazawa and Mariya Suzuki, were moved to the Shanghai affiliate.

Like the Japanese group, the Shanghai group performs in theaters and has held “general elections” in which members are ranked by popularity.