Staff at Exmouth's and Exeter crown Post Offices are set to go on strike this afternoon.
Members of the Communication Workers Union in more than 370 Crown Offices will walk out for half a day from lunchtime.
The CWU is campaigning against plans to close or franchise more than 70 Crown Offices, the larger branches usually sited in high streets, and says staff have not had a pay rise for two years.
Hundreds of jobs would be affected by the Post Office's plans, which would also hit town centres already struggling to attract businesses, the union said.
The Crown Offices handle around a fifth of Post Office business and 40% of financial services sales, said the union.
Billy Hayes, the CWU's general secretary, said: "This is effectively a Post Office closure programme in a desperate attempt to slash costs to meet Government funding cuts by 2015. The Post Office can talk about 'transformation' and 'sustainability' all it likes but the reality is that these are euphemisms for closing offices, drastically altering the make-up of the post office network and handing the running of services over to corporations which are built around other income streams and could walk away from post office services.
"These are services and as taxpayers we value them and want our taxes to bring us services we value. It's not a simple 'profit and loss' calculation. The Government is the elephant in the room here and they must be held responsible."
