NLD spokesman U Lwin said on Monday the party confirmed over the weekend that Suu Kyi had been told her detention would be extended.
He did not give further details of the order or how he learned of it. Suu Kyi's telephone has been disconnected, and party leaders have not been allowed to visit her since May.
Suu Kyi was taken into custody in May 2003 while travelling in northern Myanmar after her motorcade was attacked by a pro-government mob. She was held first by the military, then transferred to house arrest in September last year after undergoing an operation at a hospital in Yangon.
Suu Kyi has been detained several times. Her longest period of house arrest was from 1989 to 1995. The government came to power in 1988 when it crushed a pro-democracy uprising that saw Suu Kyi rise to prominence. It called elections in 1990, but refused to hand over power when the NLD won overwhelmingly.