Adam Crozier, chief executive of Royal Mail, said: "Every year, Royal Mail recruits thousands of additional fully vetted, temporary staff as part of the operation which successfully delivers the Christmas mail."
He also urged the Communications Workers Union (CWU) union to halt its appalling and unjustified attack on customers", as the intended strike action later this week approaches.
He added: "We are absolutely determined to do everything we can to minimise delays to customers’ mail, especially in the run-up to Christmas.
Speaking on BBC’s Andrew Marr programme, CWU general secretary Billy Hayes, said of the recruitment drive: "I think it is a stupid move. It will inflame things."
At the time of writing, the first nationwide postal strikes are set to take place starting this week after a "genuine offer" from the CWU was rejected by the Royal Mail.
Around 42,000 mail centre staff and network drivers will stage a 24-hour walkout on Thursday 22 October, swiftly followed by 78,000 delivery and collection staff following suit on 23 October.
Business Secretary Lord Mandelson condemned such action by Royal Mail CWU members as a "suicidal act" that "defies logic" and one that could turn customers away from the mail medium.
