Postgres how to return multiple columns in subquery

I have a simple Postgres function:

CREATE OR REPLACE FUNCTION public.drivers_have_unsatisfied_documents()
 RETURNS driver_expiring_documents
AS $function$
DECLARE
    unsatified_documents driver_expiring_documents;
    expiring_doc driver_expiring_documents%rowtype;
    expiring_doc_driver_ids text[];
    expired_doc_driver_ids text[];
    expiring_date date;
    driver_id_arg text;
BEGIN
    unsatified_documents := array(
    select expiration_date, driver_id from all_requirements_driver_documents where expiration_date <= (now() + interval '1 month')::DATE and expiration_date > (now() - interval '7 day')::DATE
    union
    select expiration_date, driver_id from all_requirements_vehicle_documents where expiration_date <= (now() + interval '1 month')::DATE and expiration_date > (now() - interval '7 day')::DATE
    );
    -- Do some more stuff, code intentionally removed ---
    return unsatified_documents;
end;
$function$ stable language 'plpgsql';

This is throws error saying

multiple columns in subquery

Can someone please help me fix it?