tmux key-binding doesn't work over ssh

Question

I am using iterm2 on a Mac, the tmux key binding works well if I start tmux locally. In particular, the Alt + arrow to switch panes.

bind -n M-Left select-pane -L
bind -n M-Right select-pane -R
bind -n M-Up select-pane -U
bind -n M-Down select-pane -D

However, the key binding no longer works when I do ssh login (to a Linux box). Any idea how to fix it? TIA