132 jobs could be lost after aluminium giant Sapa announced a consultation that could see the closure of its plant in Bedwas, near Caerphilly.
The company said it needs to remain competitive in the face of "significant changes" to its markets in recent years.
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Medication designed for animals was taken from the building in Abertillery on Thursday night.
More than a thousand riders will be taking part in a series of events in and around the town.
Some warm spells of sunshine will develop, although scattered heavy and thundery showers are also expected during the afternoon.