For multi-line labels, you have the option to adjust the default line spacing between the lines of the label.

To Adjust the line spacing:

1.Double click the label you wish to adjust. The label will be highlighted.

2.With the text selected, right click and type in your desired value in the Text Lines Spacing/Squeezing in the floater menu. Increasing the value will widen the space between lines. Decreasing the value will squeeze the space between lines.