diff --git a/cmd/cli/command.go b/cmd/cli/command.go
index eae6dfc..175839a 100644
--- a/cmd/cli/command.go
+++ b/cmd/cli/command.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
 	"os"
 
 	otlh "github.com/xifanyan/otlh/pkg"
@@ -58,6 +59,21 @@ var (
 			CheckInputOnly,
 			SkipInputCheck,
 		},
+		Before: func(c *cli.Context) error {
+			allowedTimezones := map[string]bool{
+				"CST": true,
+				"EST": true,
+				"MST": true,
+				"PST": true,
+				"UTC": true,
+			}
+
+			tz := c.String("timezone")
+			if !allowedTimezones[tz] {
+				return fmt.Errorf("timezone %s is not supported (UTC|CST|EST|MST|PST only)", tz)
+			}
+			return nil
+		},
 	}
 
 	VerifyCmd = &cli.Command{
diff --git a/cmd/cli/flag.go b/cmd/cli/flag.go
index 08450fb..b611ddc 100644
--- a/cmd/cli/flag.go
+++ b/cmd/cli/flag.go
@@ -99,7 +99,7 @@ var (
 	Timezone = &cli.StringFlag{
 		Name:    "timezone",
 		Aliases: []string{"tz"},
-		Usage:   "timezone for dates used in input file e.g., PST or EST",
+		Usage:   "timezone for dates used in input file, supproted timezones: PST|EST|MST|CST",
 		Value:   "UTC",
 	}
 )
diff --git a/pkg/utils.go b/pkg/utils.go
index b0c6810..842e384 100644
--- a/pkg/utils.go
+++ b/pkg/utils.go
@@ -115,12 +115,14 @@ func IsValidEmailAddress(email string) bool {
 
 func GetTimezoneLocation(tz string) string {
 	switch tz {
-	case "PST":
-		return "America/Los_Angeles"
+	case "CST":
+		return "America/Chicago"
 	case "EST":
 		return "America/New_York"
 	case "MST":
 		return "America/Denver"
+	case "PST":
+		return "America/Los_Angeles"
 	// Add more cases for other timezones if needed
 	default:
 		return "UTC"