Christian Solidarity Worldwide (CSW) claims the seven Protestants were taken into custody by local security officials after gathering for worship at a local pastor's home in the Savannakhet Province of the Southeast Asian state.
The group had reportedly been told the week before that such meetings were banned, despite having held similar gatherings for the last three or four years.
It is understood that the seven Christians, aged 18 to 60, are currently being detained at the Boukham village government headquarters.
Pastor Sompong Supatto is reportedly handcuffed and has been placed in leg stocks.
Research carried out by CSW between 2012 and 2014 found Savannakhet to be one of the worst provinces for violations against Protestant Christians in Laos, which include forced eviction, arrest and detention, disruption of religious meetings and services, forced participation in animist ceremonies, and threats.
CSW's chief executive, Mervyn Thomas, said: "We deplore the local authorities' decision to ban Christian worship in Boukham village, and the arrest of the seven Christians on 29th September.
"Sadly, this kind of incident is still common in Savannakhet Province and other parts of Laos, despite the government's recognition of Protestant Christianity.
"We call on the central government to protect and promote the rights of people of all religions or belief, in all parts of the country.
"We further call on the local authorities in Savannakhet Province to release the seven Christians arrested in Boukham village, and the five Christians cleared of murder in August 2014."
Also in Savannakhet, five Christians accused of the murder of a Christian convert in June this year remain in detention, despite having been found "not guilty".
Savannakhet Office of Prosecutors ruled that Pastor Kaithong and four Christians detained since 23th June had not committed any criminal offence.
However, they remain in detention as the authority to release the five detainees lies with the Atsaphangthong district chief. No date has yet been set for their release.
Recent reports claim that the health of the five Christians has deteriorated since the start of their imprisonment.