Can you help me explain why seek needs to be added with ing in this English sentence? Can you explain the syntax structure to me again?

She (subject) also (adverb) indicated (predicate) that (object clause introduced by that) the new tests for those (subject of the object clause) seeking a spousal visa (Verb-ing as a postpositioned attributive Modify those) would be made (the predicate of the object clause) more difficult (the object or slogan of the clause) in the future (time adverbial).

Here seeking is the verb -ing form as a postpositional attributive modification of those , because the action of seek is actively uttered by those, so use the -ing form; if it is passively uttered, use the past participle form of seek, seeked.