It's over recent Census results, which showed a decline in the number of Welsh speakers.
The Welsh Government say the building remains open to staff and visitors as usual.
Cymdeithas are holding a peaceful protest at one of the entrances at the Welsh Government offices in Cardiff. The main reception remains open as usual to all staff and visitors.
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A wet and windy night for much of Wales, remaining dry in the far north.
Welsh Premier League side Bangor City have been refused a license to continue playing in Welsh football's top tier.