De or het loonsuppletieregeling?

The correct Dutch article is:

de loonsuppletieregeling

Rule Words ending in -ing: almost always de. See the rule

How to use loonsuppletieregeling

the loonsuppletieregelingde loonsuppletieregeling
this loonsuppletieregelingdeze loonsuppletieregeling
that loonsuppletieregelingdie loonsuppletieregeling
our loonsuppletieregelingonze loonsuppletieregeling
your loonsuppletieregelingjouw loonsuppletieregeling
every loonsuppletieregelingelke loonsuppletieregeling
which loonsuppletieregeling?welke loonsuppletieregeling?
a big loonsuppletieregeling / the big loonsuppletieregelingeen grote loonsuppletieregeling, de grote loonsuppletieregeling