The Article 2 of the Treaty on European Union (consolidated version) says:
The Union is founded on the values of respect for human dignity, freedom, democracy, equality, the rule of law and respect for human rights
This ideological foundation is incompatible with authoritarianism. But ideologies are usually trumped by realpolitical considerations, so let's move on.
There already are considerable protests against these policies in Poland. The recent reform of the constitutional court caused spontaneous protests of tens of thousands of people to which PiS supporters responded with counter-protests of similar size. Large, opposing protests are worrisome, because they can easily escalate into full-blown street riots.
Why is that an economical factor?
Unofficial priority number one for the European Union is "free trade must not be disturbed" and riots in Poland would do exactly that. They would brand the country as politically unstable, which would deter investors and traders.
There is even a small chance that this situation might escalate into a full-blown civil war in Poland, which would - needless to say - be quite a catastrophe for the European Union. And this time there is no excuse for not taking refugees: EU citizens have complete freedom of movement in the EU.
In many European states, the governing parties currently feel an increasing competition from right-wing nationalist parties. They are afraid that should Poland be successful and unopposed with their current course of action, it might cause a ripple effect which also strengthens similar parties in their own states and erodes their own power-base.