A jury convicted defendant of assault in the fourth degree and criminal mischief in the second degree. ORS 163.160; 164.354. The issue is whether the state can prevent the court from excluding a witness, who is a city police officer, by designating the officer as the state’s representative under OEC 615(2). We reverse and remand.
This is a simple assault and criminal mischief case. The pivotal issue in the trial was whether defendant or “the victim” was the aggressor. Both testified, and they gave notably different accounts of their altercation.
Davis testified that he is a process server. After two or three unsuccessful attempts to serve documents on defendant, he went to defendant’s home and found the front door partially open. He knocked, and defendant came to the door. Davis told defendant that he had some papers for him. Defendant kicked the door closed, but the latch did not engage, and the door bounced open. Davis dropped the documents and turned to leave. As he was leaving, defendant came out and kicked him. Davis turned around and said, “I don’t want this to go any farther.” Defendant lunged at Davis and a scuffle ensued.
Defendant testified that he was awakened by a loud bang. He went to the door and saw a person (Davis) whom he did not know. Davis kicked in the door, grabbed defendant and dragged him outside. Eventually, the men separated, and Davis left.
Davis went to a nearby park to call the police. Defendant went to the police station. Both men wanted to press charges. Officer Brooks took a statement from defendant, who then went to a hospital for medical treatment. Davis arrived at the station, and Brooks took a statement from him also. After taking the witnesses’ statements, Brooks decided to cite defendant for assault.
At trial, defendant moved to exclude witnesses from the courtroom while they were not testifying. For reasons known only to the state, the prosecutor designated Brooks as the state’s representative and requested that she be allowed *493to sit at the counsel table. The court granted the state’s request.
In his first assignment of error, defendant contends that the court erred by refusing to exclude Brooks from the courtroom. The dissenting opinions contend that defendant did not preserve the purported error for appellate review.1 In State v. Hitz, 307 Or 183, 188, 766 P2d 373 (1988), the court articulated a framework for determining whether an error has been adequately preserved:
“We have previously drawn attention to the distinctions between raising an issue at trial, identifying a source for a claimed position, and making a particular argument. The first ordinarily is essential, the second less so, the third least.” (Emphasis in original; citation omitted.)
At trial, defendant argued:
“[The] police officer has no right to sit at counsel table * * *. [The Court of Appeals has] held that rule 615 requires exclusion of witnesses upon proper motion absent a showing of good cause for not excluding them. And I don’t think the state has met that burden.”
Defendant clearly objected to Brooks’ presence in the courtroom, as well as her placement at the counsel table. He identified OEC 615 as the source of law that supported his contention that she should be excluded from the courtroom.
Defendant argued:
“[Brooks is] just another witness in this case, and [she is] not a party, necessarily. * * * They’re not saying that it’s [sic] a party, they’re not saying the officer’s a victim and they’re not saying that this party is essential to the presentation of [the state’s case].”
*494That argument addressed defendant’s contention that Brooks did not fit within any of the exceptions to the general rule of OEC 615, including the exception for a witness who is “an officer or employee of a party which is not a natural person.” Defendant satisfied every requirement for preserving the purported error. State v. Hitz, supra.
The caption of defendant’s first assignment of error refers to his contention that the court erred by allowing Brooks to sit at the counsel table. An unnecessarily rigid application of ORAP 5.45 might lead to the conclusion that he has not properly presented his contention that the court erred by refusing to exclude Brooks from the courtroom. However, in the first paragraph of his argument he states, “Defendant appeals from the trial court’s failure to exclude this police officer witness.” The remainder of his argument focuses on whether the officer should have been excluded from the courtroom. He has adequately assigned the error for our review. ORAP 5.45(2), (4).
Accordingly, we turn to the merits of defendant’s first assignment of error. OEC 615 provides:
“At the request of a party the court may order witnesses excluded until the time of final argument, and it may make the order of its own motion. This rule does not authorize exclusion of (1) a party who is a natural person, or (2) an officer or employee of a party which is not a natural person designated as its representative by its attorney, or (3) a person who whose presence is shown by a party to be essential to the presentation of the party’s cause, or (4) the victim in a criminal case.”
In general, a decision whether to exclude witnesses is within the court’s discretion, because OEC 615 provides that “the court may order witnesses excluded.” (Emphasis supplied.) By using the term “may” in the rule, the legislature intended courts to have discretion in deciding whether to exclude witnesses. State v. Harding, 116 Or App 29, 32 n 4, 840 P2d 113 (1992); see State v. Ede, 167 Or 640, 642-43, 117 P2d 235 (1941).2 However, OEC 615 “does not authorize exclusion” *495of witnesses who fall into one of four categories of exceptions. It does not give the court discretion to exclude them.3 Whether a party can designate a witness as its “representative” under OEC 615(2) is a question of law.
OEC 615(2) provides that “an officer or employee of a party which is not a natural person” may be designated as a representative. Brooks was an employee of the City of Ash-land. See ORS 237.610. The City of Ashland is not a party in this case — the State of Oregon is. Brooks was neither an officer nor an employee of the state.
The state apparently believes that it can designate any witness it desires as its “representative” and the court is without authority to exclude that witness from the courtroom. The legislature could not have intended to permit a litigant to abrogate a statute at will. A party that is not a natural person may designate a witness as its representative only if it establishes that the witness is actually an officer or an employee of the party. The state did not make that showing, nor could it.
Brooks was not one of the four types of witnesses who are exempt from exclusion under OEC 615. The court was therefore required to exercise its discretion in deciding whether to exclude her from the courtroom. However, the court did not exercise its discretion, because it mistakenly concluded that it had no authority to exclude her. The court’s failure to exercise its discretion constituted an error. Because of the difficulty of showing that the testimony of one witness has been influenced by the testimony of another, we presume that defendant was prejudiced by Brooks’ presence in the courtroom, “unless the record affirmatively reflects the contrary.” State v. Cetto, 66 Or App 337, 340, 674 P2d 66, rev den 296 Or 712 (1984). Nothing in this record negates that presumption.
*496To the contrary, the record reflects that the prejudice was compounded. Brooks testified after sitting through the testimony of the state’s other witnesses, and she testified again on rebuttal after hearing defendant’s entire case. See State v. Vosika, 83 Or App 298, 302, 731 P2d 449, clarified 85 Or App 148, 735 P2d 1273 (1987); State v. Ott, 61 Or App 576, 583, 659 P2d 388 (1983), rev’d on other grounds 297 Or 375, 686 P2d 1001 (1984).
Defendant also contends that the court erred by not granting a mistrial. Because we conclude that defendant is entitled to a new trial, we need not address that assignment of error.
Reversed and remanded for a new trial.
ORAP 5.45 provides, in part:
“(2) No matter assigned as error will be considered on appeal unless it was preserved in the lower court and assign as error in the party’s opening brief; provided that the appellate court may consider errors of law apparent on the face of the record.
“(4) Each assignment of error shall be clearly and concisely stated under a separate and appropriate heading, must be specific and must set our verbatim the pertinent portions of the record, if it relates to a specific ruling that is being challenged.”
Ede was decided under OCLA § 4-702, which provided:
“If either party require it, the judge may exclude from the courtroom, any witness of the adverse party not at the time under examination, so that he may not hear the testimony of other witnesses.”
*495OCLA § 4-702 was codified at former ORS 45.510 in 1953, which was repealed in 1981, when the legislature adopted OEC 615. Or Laws 1981, ch 892, §§ 56, 98.
We express no opinion whether any other rule of law authorizes a court to exclude a witness who falls within one of the exceptions listed in OEC 615. We also express no opinion whether any rule of law authorizes a trial court to “veto” the designation of a representative who is an officer or an employee ofapartythatisnota natural person. See 120 Or App at 497.