lock my FPS camera or direct it to face z

what I am doing is making it so when the player stands in front of a ladder he climbs it when you hit the E key. He is actually standing on a platform that slowly animates upwards. Basically it looks like he is riding an elevator instead of climbing a ladder. I want the camera to face the ladder ( which is looking straight ahead up the z axis - the y rotation is zero). I have tried various LookAt scripts and quaternion rotation and even just "simply" setting the transform rotation to zero ( but Unity won't let me). So the question is...how do I get the camera to face the ladder. Currently I have it so the horizontal Sensitivity of my mouse goes to Zero so I can make it so I can't rotate, but I want to call that function only after I have turned to face the ladder. Here is the script I have so far. Obviously the sensitivity change will need to happen AFTER I face the correct direction. The ladder is in a little alcove so the player is kind of forced to face it, but there is the possibility of him turning to one side or the other before hitting the E key

 using UnityEngine;
 using System.Collections;
 
 public class climbLadder : MonoBehaviour {
     Animator anim;
     public Transform that;
 
     void Start () {
         anim = GetComponent<Animator>();
     }
     void OnTriggerEnter(Collider other)
     {
         if(other.tag == "Player")
         {
             if (Input.GetKeyDown(KeyCode.E))
             {
             anim.SetTrigger ("Climb");
                 FPSCamera.horizontalSensitivity2 = 0;
                 //FPSCamera.viewTarget2 = that;
         }
     }
 }
 
 void OnTriggerExit(Collider other)
 {
     if(other.tag == "Player")
         {
         anim.ResetTrigger ("Climb");
     anim.SetTrigger ("leave");
             FPSCamera.horizontalSensitivity2 = 250;
         }
     }
 }