Exiled religious leaders have accused authorities in Vietnam of hounding believers and choking freedom of worship.
Christian and Buddhist leaders have told the United States Commission on International Religious Freedom in Washington that Vietnam's communist rulers are determined to retain tight control over religion and dissent.
They urged the U-S Congress to shelve an historic trade pact signed last year with Hanoi, until its record improves.
Hanoi has branded the hearing as gross interference in its affairs and comes as Congress prepares for a debate on whether to ratify the trade pact.
The hearing follows a wave of unrest in Vietnam's mainly Christian central highlands, fuelled by the seizure of church buildings by the authorities.
The Reverend John Tran Cong Nghi, of the VietCatholic network, said there was no freedom of religion, because it's controlled by government authorities at all levels.
An exiled spokesman of the Unified Buddhist Church of Vietnam, Vo Van Ai, cited an alarming scale of repression against Buddhism in Vietnam.
(14:12:16 AEST)