The dispute follows the company’s decision not to reinstate David Mitchell, 57, despite being ordered to do so by an employment tribunal judge.
Mr Mitchell, from Cupar in Fife, who has 27 years of service, was sacked in December 2014 after “test” items went missing. Mr Mitchell’s van, car and house was searched, but no evidence was found.
Postal workers in Cupar held a one-day strike a week before Christmas with a 24-hour day of action planned for Monday.
Kenny Logan, CWU branch secretary, said: “I’m concerned for our members in future tribunals and the ability of the business conducting future conduct cases. We’re determined to win reinstatement for David. If this doesn’t happen, this could escalate to a branch-wide dispute.”
Customers held “silent protests” outside the Cupar delivery office. Stephen Gethins, SNP MSP for North East Fife has also backed Mr Mitchell. Mr Mitchell, said: “I didn’t want it to come to this. I just wish the Royal Mail could see sense and give me my job back.”
A Royal Mail spokeswoman said: “Royal Mail was ordered by the tribunal to pay Mr Mitchell a compensatory award plus some of the costs in this case, as we do not believe that it is appropriate for him to return to work with us. This payment has been paid to him.
“We take the security of mail extremely seriously and investigate all complaints.”