Post office staff had passed the snake around for about 8 hours before it was about to be put on a plane at Stansted Airport.
The animal's owner had sold it on ebay - and then attempted to post it from Harlow to Exeter.
The move is a breach of Royal Mail rules on transporting live animals.
RSPCS inspector Steve Reeves told the Mirror: "All the machine picked up was that there was something organic in the shape of a snake – so they must have got quite a shock when they opened up the package."
He added: "Snakes are very sensitive to their environment. It could suffer if it was put into a cold place like an airplane hold."
The new owner has now arranged for the snake to be picked up by courier.
The GMB union has said that 150 of its members employed by Swissport have voted for the action, claiming that shift changes would lead to wage cuts of up to £1,000.
Family holidays could be left severely disrupted, with the strikes being carried out on Good Friday, Easter Saturday and Easter Monday.
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