diff --git a/pr/webhook/pull_request.go b/pr/webhook/pull_request.go
index e1775b0..1f80d17 100644
--- a/pr/webhook/pull_request.go
+++ b/pr/webhook/pull_request.go
@@ -163,6 +163,16 @@ func (receiver *Receiver) handlePullRequest(body []byte) {
 		}
 		newLabels = append(newLabels, typeLabels...)
 
+		receiver.membersLock.RLock()
+		members := receiver.members
+		receiver.membersLock.RUnlock()
+		if members != nil {
+			_, exist := (*members)[*event.Sender.Login]
+			if exist {
+				newLabels = appendIfUnique(newLabels, "by: member")
+			}
+		}
+
 		err = receiver.githubClient.ReplaceLabels(owner, repo, number, newLabels)
 		if err != nil {
 			log.Println(err)
diff --git a/pr/webhook/server.go b/pr/webhook/server.go
index a36dae8..1e637e8 100644
--- a/pr/webhook/server.go
+++ b/pr/webhook/server.go
@@ -7,6 +7,8 @@ import (
 	"io/ioutil"
 	"net/http"
 	"strings"
+	"sync"
+	"time"
 
 	"github.com/macports/mpbot-github/pr/db"
 	"github.com/macports/mpbot-github/pr/githubapi"
@@ -19,6 +21,8 @@ type Receiver struct {
 	testing      bool
 	githubClient githubapi.Client
 	dbHelper     db.DBHelper
+	members      *map[string]bool
+	membersLock  sync.RWMutex
 }
 
 func NewReceiver(listenAddr string, hookSecret []byte, botSecret string, production bool, dbHelper db.DBHelper) *Receiver {
@@ -71,9 +75,36 @@ func (receiver *Receiver) Start() {
 		w.WriteHeader(http.StatusNoContent)
 	})
 
+	go receiver.updateMembers()
+
 	http.ListenAndServe(receiver.listenAddr, mux)
 }
 
+func (receiver *Receiver) updateMembers() {
+	for ; ; time.Sleep(24 * time.Hour) {
+		users, err := receiver.githubClient.ListOrgMembers("macports")
+		if err != nil {
+			continue
+		}
+		members := make(map[string]bool)
+		for _, user := range users {
+			if user.Login == nil {
+				continue
+			}
+			login := *user.Login
+			if login == "" {
+				continue
+			}
+			members[login] = true
+		}
+		if len(members) > 0 {
+			receiver.membersLock.Lock()
+			receiver.members = &members
+			receiver.membersLock.Unlock()
+		}
+	}
+}
+
 // checkMAC reports whether messageMAC is a valid HMAC tag for message.
 func (receiver *Receiver) checkMAC(message, messageMAC []byte) bool {
 	mac := hmac.New(sha1.New, receiver.hookSecret)