Apple was pressed on Thursday to take action on Vietnam's detention of climate experts, with activist organizations saying it should weigh in given that the country has become a key manufacturing hub for the iPhone-maker.

In a letter to Apple, more than 60 human rights and environmental rights organizations highlighted the Sept. 15 detention of Ngo Thi To Nhien, the executive director of the Vietnam Initiative for Energy Transition (VIET), an independent think tank focused on green energy policy.

Before her detention, Nhien had worked with the Vietnamese government and international organizations on the country’s energy transition towards renewable energy, according to Bangkok-based advocacy group Project88, one of the rights groups that signed the letter.