Short and sweet: they are allowed to do that. So save yourself the money for a lawyer
Rhenish greetings from on the road
Bauexperte
Oh?
And on what legal basis, Ms. Lawyer?
Of course, it is possible that the city has contractually been granted such a right, or via a building encumbrance, but the original poster would know about that, wouldn't they?
If you look, you'll find dozens of court rulings where such retaining walls had to be removed again. A very famous one from last year in Dortmund ended with a settlement..
There are definitely construction solutions that make such a retaining wall unnecessary on foreign ground. Just costs 3 Marks more.