Perhaps you should try some spelling variations:
"vakbond/mijnwerkers | syndicaats/mineurs" » "vakbond/mijnwerkers | syndicaat/mineurs"
"vakbonden/mijnwerkers | syndicat/mineurs" » "vakbonden/mijnwerkers | syndicaat/mineurs", "vakbonden/mijnwerkers | syndicale/mineurs"
"vakbonden/mijnwerkers | syndicats/mineurs" » "vakbonden/mijnwerkers | syndicaats/mineurs", "vakbonden/mijnwerkers | syndicales/mineurs", "vakbonden/mijnwerkers | syndicale/mineurs", "vakbonden/mijnwerkers | syndicaat/mineurs"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("vakbond/mijnwerkers | syndicaats/mineurs") OR ((("vakbonden/mijnwerkers | syndicat/mineurs") OR ("vakbonden/mijnwerkers | syndicats/mineurs"))))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"vakbond/mijnwerkers | syndicaats/mineurs\") OR (((\"vakbonden/mijnwerkers | syndicat/mineurs\") OR (\"vakbonden/mijnwerkers | syndicats/mineurs\"))))".
• Removing quotes may allow a broader search: (( vakbond/mijnwerkers | syndicaats/mineurs ) OR ((( vakbonden/mijnwerkers | syndicat/mineurs ) OR ( vakbonden/mijnwerkers | syndicats/mineurs )))).
• Adding a wildcard symbol may retrieve word variants: (("vakbond/mijnwerkers | syndicaats/mineurs") OR ((("vakbonden/mijnwerkers | syndicat/mineurs") OR ("vakbonden/mijnwerkers | syndicats/mineurs"))))*.