Andy Furey is the National Officer for Communication Workers Union, which represents staff working in Crown Post Offices.
He told ITV News: "A Welsh town like Holywell needs a Crown Post Office. If we lose it, this could be the death knell for the high street in Holywell."
More top news
Wales are through to the Rugby World Cup quarter-finals after Australia beat England at Twickenham last night.
The Conservative's annual conference is getting underway in Manchester, and talk has turned to next year's Welsh election.
A band of showery rain will push through overnight, but it will feel mild.