Anyone working in or employing someone in Austria must comply with the applicable labour legislation. Whether you work as self-employed contractor or an employee depends on the specific conditions under which the work is performed and not on any single agreement between the parties.
In practice however, things are often tricky, as many people who qualify as blue-collar workers or as employees, work on a contract-for-services basis as self-employed persons. In the case of self-employed work the principal's risk is reduced, on the one hand, because all entitlements an employee has, such as annual leave, sick benefits, etc., do not apply to the contract for services. On the other hand, for some employers it is sheerly impossible - particularly in the artistic industry - to employ someone, because the terms of an employment contract in Austria are economically prohibitive for many, owing to high non-wage labour costs or minimum wages set by collective-bargaining agreements.