Tran Thi Hong claims local authorities in Gia Lai province used violence to stop her meeting the US Ambassador At Large on International Religious Freedom on March, 31.
The meeting with David Saperstein was re-arranged to Mrs Hong's home on April, 14 but plain-clothes agents allegedly abducted her and severly beat her.
Tran Thi Hong belongs to the Vietnamese Women for Human Rights group and is married to Pastor Nguyen Cong Chinh, an activist currently serving an eleven-year jail sentence.
Pastor Chinh, who was convicted of "undermining national unity" in 2012, advocated for religious freedom and democracy in Vietnam, and helped offer help to ethnic minorities and the families of prisoners of conscience.
Ambassador Saperstein is reported as confirming to Radio Free Asia that authorities blocked Mrs Hong's entry to the hotel where she was due to meet the diplomat on March, 31.
CSW has joined 32 Vietnamese faith-based organisations, international human rights NGOs and individuals in supporting a statement concerning Mrs Hong.
CSW's Chief Executive Mervyn Thomas said: "We fully support this statement calling on Vietnam's government to investigate allegations of torture of Tran Thi Hong.
"CSW continues to receive reports of harassment, intimidation and violence against religious communities not registered with the authorities; we further note various violations against bloggers, religious leaders, lawyers and activists seeking to promote human rights in Vietnam.
"We call on the government to investigate these deeply concerning reports of violence against Tran Thi Hong, and to release Pastor Nguyen Cong Chinh and other prisoners detained for defending the freedom of religion or belief and other human rights".