There are quite a lot of ways you can do that: particularly if you set up an array or list of "allowed values" - which can be a static readonly list.
The first is to use a switch instead:
string StatusOfCondition = "26";
switch (StatusOfCondition)
{
case "26":
case "28":
case "34":
break;
default:
break;
}
The framework can optimise switches pretty well.
The array version may be better though:
private static readonly string[] allowedValues = new string[] { "26", "28", "34" };
...
string StatusOfCondition = "26";
if (allowedValues.Contains(StatusOfCondition))
{
...
}