diff --git a/cmd/server/main.go b/cmd/server/main.go
index 715dad4..8d514cd 100644
--- a/cmd/server/main.go
+++ b/cmd/server/main.go
@@ -52,6 +52,7 @@ func main() {
 	r.HandleFunc("/retries", retries.HandleRetries).Methods(http.MethodGet, http.MethodPost)
 	r.HandleFunc("/retries/after", retries.HandleRetries).Methods(http.MethodGet)
 	r.HandleFunc("/errors/{status_code}", errors.HandleErrors).Methods(http.MethodGet, http.MethodPost)
+	r.HandleFunc("/errors/union/{tag}", errors.HandleErrorsUnion).Methods(http.MethodGet)
 	r.HandleFunc("/optional", acceptHeaders.HandleAcceptHeaderMultiplexing).Methods(http.MethodGet)
 	r.HandleFunc("/readonlyorwriteonly", readonlywriteonly.HandleReadOrWrite).Methods(http.MethodPost)
 	r.HandleFunc("/readonlyandwriteonly", readonlywriteonly.HandleReadAndWrite).Methods(http.MethodPost)
diff --git a/internal/errors/service.go b/internal/errors/service.go
index 85bbd08..8f6df5d 100644
--- a/internal/errors/service.go
+++ b/internal/errors/service.go
@@ -1,6 +1,7 @@
 package errors
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -55,3 +56,84 @@ func HandleErrors(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 }
+
+// Returns one of an errors union with a 400 Bad Request status, based on the
+// provided tag name in the path parameters with these response schemas:
+//
+//	taggedError1:
+//	  type: object
+//	  properties:
+//	    tag:
+//	      type: string
+//	      enum: [tag1]
+//	    error:
+//	      type: string
+//	  required:
+//	    - tag
+//	    - error
+//	taggedError2:
+//	  type: object
+//	    properties:
+//	      tag:
+//	        type: string
+//	        const: tag2
+//	      error:
+//	        type: object
+//	        properties:
+//	          message:
+//	            type: string
+//	        required:
+//	          - message
+//	    required:
+//	      - tag
+//	      - error
+func HandleErrorsUnion(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	tag, ok := vars["tag"]
+
+	if !ok {
+		utils.HandleError(w, fmt.Errorf("tag path parameter is required"))
+		return
+	}
+
+	if tag != "tag1" && tag != "tag2" {
+		utils.HandleError(w, fmt.Errorf("tag path parameter must be either tag1 or tag2"))
+		return
+	}
+
+	var errorRes any
+	var responseBody bytes.Buffer
+
+	if tag == "tag1" {
+		errorRes = struct {
+			Tag   string `json:"tag"`
+			Error string `json:"error"`
+		}{
+			Tag:   "tag1",
+			Error: "intentional tag1 error",
+		}
+	} else {
+		errorRes = struct {
+			Tag   string `json:"tag"`
+			Error struct {
+				Message string `json:"message"`
+			} `json:"error"`
+		}{
+			Tag: "tag2",
+			Error: struct {
+				Message string `json:"message"`
+			}{
+				Message: "intentional tag2 error",
+			},
+		}
+	}
+
+	if err := json.NewEncoder(&responseBody).Encode(errorRes); err != nil {
+		utils.HandleError(w, err)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusBadRequest)
+	_, _ = w.Write(responseBody.Bytes())
+}