UDD chairwoman Tida Tawornseth said the gathering aimed at mobilising supporters in the North and Northeast would take place at the Chiang Mai 700 Year Stadium.
UDD leaders would start addressing demonstrators at 6pm and the event is expected to end at 2am Sunday, she said.
The red-shirt leader repeated the fact that the UDD dose not agree with the idea of separating Thailand and demanded that PDRC secretary-general Suthep Thaugsuban stop accusing the movement of supporting segregation. The UDD would face nationwide opposition if it fostered such idea, she added.
The latest round of UDD counter protests against the anti-government PDRC began on Saturday at Thung Sri Muang in Udon Thani with a gathering of red-shirts from eight upper northeastern provinces. The rally ended on Sunday after the group moved on to Kalasin, Maha Sarakham and Khon Kaen.
Ms Tida earlier said red-shirts were yet to decide whether to come and protest in Bangkok, claiming that it depends on the ongoing political situation.