Among the civilian staff taking part are PCSOs, custody and detention officers, front counter and 999 control centre staff.
Staff formed a picket outside Worksop Police Station this morning.
Roger Young, regional organiser for UNISON, said the union expected more staff to walk out today compared with Tuesday.
Notts Police said 135 members of staff walked out on strike today but that it was not having a major impact on the force’s ability to provide an effective service.
Since Wednesday members are also staging a work-to-rule.