How did relations between Prussia and the Austrian empire begin to change after the Zollverein in Germany?

After the creation of the Zollverein, the relations
between Austria and Prussia became even more contentious than they had
been.

The creation of the Zollverein was meant in large
part to strengthen Prussia.  Prussia was in competition with Austria for influence over
the various German states that existed at the time.  By creating the Zollverein, Prussia
pulled the German states into a closer relationship with it and away from a relationship
with Austria.  This exacerbated tensions with Austria because Austria was worried about
its loss of influence over the German states as those states gravitated towards
Prussia.

In this way, the creation of the Zollverein made
relations between Prussia and Austria more hostile and tense.