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Is the step inside the condo and so in the area clearly owned by you or is it part of the common area?
They do not have the right to simply enter your premises without appropriate notice or consent as there was no emergency and they did not have the right to install anything in your home without your express consent.
I suggest that you demand they rectify the situation at once and so that there is no damage caused by what they did.
I cannot review the building code. That is too detailed in terms of expecting an answer on this site.
But maybe another lawyer will want to answer so I will opt out.