The Pretoria Zoo has failed in a last-ditch bid to prevent a strike.
The National Trade Union Congress slapped a strike notice on the National Zoological Gardens of SA yesterday.
Zoo spokesman Craig Allenby said the notice warned that members of the union, which represents about 120 zoo workers, intended demonstrating and picketing after the expiry of the 48-hour notice period.
He said the dispute related to an agreement signed in 2009 between the zoo and its trade unions on the implementation of a seven-day working week.
"[The union] is demanding that the agreement be cancelled and employees be paid overtime for weekend work."
Management emphasised that the zoo - which attracts more than 150000 children annually - was a seven-days-a-week operation and it was impractical and financially impossible to meet the demands of the union.
Founded in 1899, the zoo is the largest and oldest in the country. It is home to more than 5000 animal species - many of them endangered.
Allenby said the zoo had the biggest inland marine aquarium in the country.
"Our animal collection includes the big five, Komodo dragons, okapi, gorillas and various birds and reptiles.
"We even have a ragged-tooth shark in the aquarium."
Management said the welfare of the animals and the safety of visitors would not be compromised.