The strike will be held by those working as warehouse stock controllers, cooks, canteen staff, and administrators for the Bradford-headquartered company.
Staff are to walkout first on 23 May until 26 May, with the second round of strike action planned for between the 13 and 16 June.
It follows a ballot where members voted “overwhelmingly” to walkout, a Unite spokesman said.
The union claimed workers were being forced to increase their pension contributions, while the supermarket reduces its own contributions, which could leave members about £500 worse off.
Other issues in dispute include the removal of a long service award, enforced job role changes, and the implementation of a new “pick rate” which dictates the speed items must be packed from shelves.
Unite national officer Adrian Jones said Morrisons had “refused to negotiate” and would now “witness the anger and ill-feeling of our members”.
Ms Graham described the pensions changes as “flagrant profiteering”, adding the supermarket was “raking in massive profits”.
