Social security Regular Expression validator in asp.net

i want to use regular expression to validate SSN with dashes. This is the format i would like to see: 000-00-0000. This expression does not work for me for some reason.

  <asp:RegularExpressionValidator runat="server" Display="Dynamic" ValidationExpression="^(\\d{3}-\\d{2}-\\d{4}|\\d{9})$" ControlToValidate="txtSSN" ForeColor="Red" />