The group, which includes the Oakland chapter of the National Association for the Advancement of Colored People, is asking for a meeting with Thao this week "to discuss this urgent matter."
The NAACP and others including Oakland City Councilmember Noel Gallo are concerned crime is rising while the chief is on leave. Armstrong is on leave following allegations of police misconduct in his department.
In a letter, NAACP President Cynthia Adams wrote: "It's like when a teacher goes on leave. The students get a sub and start acting up. Oakland is acting up."
Adams urged Thao to listen to the voters and communities of her city and reinstate Armstrong.
Adams in her letter said she is pleased after learning that Thao will consider all relevant information and meet or speak with "key decision makers and community constituents."
Thao did not immediately respond to a request for comment on the continued call for Armstrong's reinstatement.
