What is the CA Civil Code that states that a corporation has to be represented in a Civil trial?

I do not believe there is a Civil Code section which requires it. However, there is well-established in the case law, at least to the extent you pursue the corporation in a limited or unlimited civil action (there is a statutory exception, at Code of Civil Procedure section 116.510 et seq., providing that a corporation can appear pro per in a small claims action by sending a corporate representative). The lead case on this is Paradise v. Nowlin (1948) 86 Cal.App.2d 897. Subsequent cases have affirmed its holding that corporations cannot appear pro per for three distinct reasons: (1) any representative sent on behalf of the corporation would be engaged in the unauthorized practice of law; (2) the rule ensures that qualified professionals will appear in court, thereby increasing the efficient and proper administration of justice; and (3) the distinction helps to maintain the wall between the corporation as an entity and its individuals shareholders, directors, and officers. (Id.; see also CLD Construction, Inc. v. City of San Ramon (2004) 120 Cal.App.4th 765, 773.) Hope that helps.

Not a Civil Code section. Rather, it is a long-standing common law rule of procedure, a corporation, unlike a natural person, cannot represent itself before courts of record in propria persona, nor can it represent itself through a corporate officer, director or other employee who is not an attorney. It must be represented by licensed counsel in proceedings before courts of record. (Caressa Camille, Inc. v. Alcoholic Beverage Control Appeals Bd. (2002) 99 Cal.App.4th 1094, 1101-1103 & citations therein.) If the corporate agent who would likely appear on behalf of the corporation in court proceedings, e.g., an officer or director, is not an attorney, that person would actually be engaged in the unlicensed practice of law. (Merco Constr. Engineers, Inc. v. Municipal Court (1978) 21 Cal.3d 724, 730.) A corporation is not a natural person, and therefore cannot appear in an action in propria persona. It can appear only through counsel. (Merco Construction Engineers, Inc. v. Mun.Ct. (Sully Miller Contracting Co.) (1978) 21 Cal.3d 724, 731.) This prohibition stems from the notion a corporate representative who would likely appear on behalf of the corporation would be engaged in the unlicensed practice of law. (Gamet v. Blanchard (2001) 91 Cal.App.4th 1276, 1284.) The prohibition against a corporation's “self-representation” in court also furthers the efficient administration of justice by assuring that qualified professionals present the corporation's case and assist the court in resolution of the issues; and it helps maintain the distinction between the corporation and its shareholders. (CLD Const., Inc. v. City of San Ramon (2004) 120 Cal.App.4th 1141, 1146.) In California, corporations must be in good standing in order to participate in litigation in any court. Moreover, corporations must be represented by counsel in litigation. California case law has held that a corporation cannot represent itself in court, either in propria persona or through an officer or agent who is not an attorney. (Merco Constr. Engineers, Inc. v. Municipal Court (1978) 21 Cal. 3d 724, 729.) See also Van Gundy v. Camelot Resorts, Inc. (1983) 152 Cal.App.3d Supp. 29, 32; and Gamet v. Blanchard (2001) 91 Cal.App.4th 1276, 1284, n. 5; Corporations Code sections 17003, 17101; PacLink Communications Internat., Inc. v. Superior Court (2001) 90 Cal.App.4th 958, 963; Grosset v. Wenaas (2008) 42 Cal.4th 1100, 1108.) A corporation is not a natural person, and therefore cannot appear in an action in propria persona. It can appear only through counsel. (Merco Construction Engineers, Inc. v. Mun.Ct. (Sully Miller Contracting Co.) (1978) 21 Cal.3d 724, 731.) This prohibition stems from the notion a corporate representative who would likely appear on behalf of the corporation would be engaged in the unlicensed practice of law. (Gamet v. Blanchard (2001) 91 Cal.App.4th 1276, 1284.) The prohibition against a corporation's “self-representation” in court also furthers the efficient administration of justice by assuring that qualified professionals present the corporation's case and assist the court in resolution of the issues; and it helps maintain the distinction between the corporation and its shareholders. (CLD Const., Inc. v. City of San Ramon (2004) 120 Cal.App.4th 1141, 1146.) A motion to strike under Code of Civil Procedure section 435 et seq. is traditionally used to reach pleading defects that are not subject to demurrer. (CLD Construction, Inc. v. City of San Ramon (2004) 120 Cal. App. 4th 1141, 1146 [striking complaint subscribed only by non-attorney president], citing 5 Witkin, Cal. Proc., 4th ed., Pleading, § 960, p. 420.) This rule appears to be the law throughout the United States. In Rowland v. California Men's Colony, Unit II Men's Advisory Council, 506 U.S. 194, 113 S.Ct. 716, 121 L.Ed.2d 656 (1993), the U.S. Supreme Court indicated that artificial entities must appear by counsel.

If the appeal is going to be heard by the labor commissioner, then I think they will allow a corporation to appear without an attorney. If the appeal is to the superior court, then they will need an attorney. In the event that they appear without an attorney, or attempt to, you should respond by filing a motion to strike whatever pleading they file. Good luck