The strike, by members of Prospect and the Public and Commercial Services union, will take place on Tuesday December 20.
The combined action by members of both unions will result in cases being postponed with some courts remaining closed for the day.
It marks the beginning of a campaign of industrial action in protest at a below inflation pay offer, which will continue with a work-to-rule and possible further strike action.
However, both unions have agreed a series of exemptions for staff if public safety is considered to be at risk.
Announcing the date, Prospect National Secretary Alan Leighton said: "Our members are not eager to disrupt the smooth running of the magistrates’ courts but feel forced into taking action because they are having to bear the brunt of a lack of funding to cover the start-up costs of HMCS."
Prospect represents over 115 court members in managerial and legal roles such as justices’ clerks, assistant justices’ clerks, senior legal advisors and bench legal managers. They will be joining picket lines outside courts across England and Wales.