California Code, Family Code - FAM § 2063

(a) The employee benefit plan shall file and serve a copy of a notice of appearance upon the party requesting joinder within 30 days of the date of the service upon the plan of a copy of the joinder request and summons.

(b) The employee benefit plan may, but need not, file an appropriate responsive pleading with its notice of appearance. If the plan does not file a responsive pleading, all statements of fact and requests for relief contained in any pleading served on the plan are deemed to be controverted by the plan's notice of appearance.