The seven are Wan Chai district councillors Clarisse Yeung and Leung Pak-kin, Eastern district councillors Wei Siu-lik, So Yat-hang, Chan Wing-tai, and Lai Tsz-yan, and Southern district councillor Michael Pang.
Yeung and Pang have both been charged with violating the national security law after taking part in a primary election organised last year.
The seven had sworn pledges of allegiance on September 10 among 24 other district councillors.
However, the oath administrator, Home Affairs Secretary Caspar Tsui, ruled that their oaths were “questionable”, and requested additional information by the following Monday so he could determine their validity.
The government said oath takers must sincerely believe in and strictly abide by oath prescribed in law, and if the oath is determined to be invalid then no arrangement shall be made for it to be retaken.