The protests were set to take place in 21 cities.
Employees unaffiliated to trade unions want pay rises of PLN 1,000 (USD 248, EUR 232) a month gross.
They are currently paid PLN 1,500 net a month on average, Polish Radio reported.
The protestors also want a reorganization of postal areas and restoration of some bonuses.
After the protests the workers were to hand in a petition to post office bosses.