Job centres in Southampton and Winchester could close or will offer limited services under a skeleton staff the PCS union said, while people ringing call centres for job advice may be met by recorded messages.
Tax offices in Southampton, Portsmouth and Winchester are also set to be hit by the walkouts, causing disruption to tax processing and other services.
The Department for Work & Pensions said the vast majority of job centres would stay open, and staff had been preparing for the disruption by reducing the number of appointments for Wednesday.
A DWP spokesman said: “We have business continuity measures in place to deliver and maintain a service for the public. We expect everyone who is entitled to benefits will receive them.”
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