The letter, signed by more than 100 members of Congress, assails the Good Friday arrest of Bishop Cosmas Shi Enxiang, reported by the U.S.-based Cardinal Kung Foundation.
The lawmakers urged China to «recognize that freedom of worship and the freedom of speech are basic human rights to be protected, not silenced.»
About a dozen bishops are now held by the Communist leaders in Beijing, which broke off relations with the Vatican in 1958.
The Cardinal Kung Foundation said in a statement Monday that the 79-year-old Shi was detained during a visit to the Chinese capital. A local police spokesman denied Shi´s arrest, but said he had been on their wanted list since 1996.