Generally speaking, the parties may agree on the nature of rights and obligations arising out of the agreement. Those rights and obligations are typically set out within the text of the contract itself, although that does not preclude the application of the general terms and conditions to which the agreement may refer. These general terms and conditions may be written by either party to the agreement or by the third party (e.g. by a professional organization). The principle of autonomy of will, as well as other related principles, allows us to deduce that the above-mentioned can be applicable in practice.
On the other hand, the use of the general terms and conditions is not without certain limits. As far as consumer agreements are concerned, they must not contain provisions that are contrary to the principle of good faith and create a significant imbalance in rights and obligations of the parties to the detriment of the consumer (Section 56 of the Act No. 40/1964 Coll., the Civil Code and Section 1813 of Act No. 89/2012 Coll., the new Civil Code). In practice, especially in case of standard form contracts, the wording of the agreement must be clear and logically organized enough for an average customer to understand the content and the meaning of the agreement. For example, a sufficient font size must be used, the most important or related provisions must be put together and not separately, etc. As stated above, despite the fact that the parties may generally use the general terms and conditions even in consumer agreements, there are not only formal, but also contextual limitations of the general terms and conditions in consumer agreements.
Therefore, in consumer agreements, the provision governing a contractual penalty may not be a part of the general terms an condition. The only way is to have the provision about the contractual penalty directly in the agreement itself (i.e. in the document to which the consumer attaches his /her signature).