You can constrain an individual axis with the Scale constraint. For example, you can scale only an object’s Y-axis.

To constrain a single axis:

1. Double-click the Scale constraint in the Scene browser to select it.
2. Open the Properties window. The Scale constraint settings display.
3. Expand Constraint Axes and disable the X, Y, or Z axis for the desired translation effect you want to inhibit.
4. To reactivate the unconstrained axes, activate the option.