What does the cryptic crossword clue "Trouble afoot after leader’s ousted in Labour organisation (5)" mean?

The definition is "Trouble". The wordplay uses a deletion. UNION (deletion) = UNION; definition: "Trouble afoot" The answer is UNION.

Trouble afoot after leader’s ousted in Labour organisation (5)

Guardian Cryptic #29605 | 26 Across | 2025-01-30 flower