The two-day action will begin on Sunday and follows a 48-hour walk-out last week by around 100 staff at 13 council-run care homes in the city.
According to Unison, changes to pay and conditions may leave some staff almost £1500 a year worse off. The council has said staff would not have basic salary cut, but some may lose shift allowances.
A Unison spokesman said: "Senior social work management still refuse to move on any aspect of the dispute. They remain unwilling to address the cut in living standards and showed little understanding, or indeed care, about what a £1500 cut in pay means to workers earning around or below average wages."
A council spokesman said: "We are again surprised and disappointed that Unison is going on strike when there is so little support from within their membership for this action."
Both sides have lodged formal complaints over allegations of the behaviour of Unison members at last week's pickets, including wearing balaclavas.