1. The Czech Republic, the Republic of Estonia, the Republic of Cyprus, the Republic of Latvia, the Republic of Lithuania, the Republic of Hungary, the Republic of Malta, the Republic of Poland, the Republic of Slovenia and the Slovak Republic hereby become members of the European Union and Parties to the Treaties on which the Union is founded as amended or supplemented.
2. The conditions of admission and the adjustments to the Treaties on which the Union is founded, entailed by such admission, are set out in the Act annexed to this Treaty. The provisions of that Act shall form an integral part of this Treaty.
3. The provisions concerning the rights and obligations of the Member States and the powers and jurisdiction of the institutions of the Union as set out in the Treaties referred to in paragraph 1 shall apply in respect of this Treaty.
See also: Treaty of Lisbon, which Poland also signed. Specifically, Declaration 17: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A...
17. Declaration concerning primacy
The Conference recalls that, in accordance with well settled case law of the Court of Justice of the European Union, the Treaties and the law adopted by the Union on the basis of the Treaties have primacy over the law of Member States, under the conditions laid down by the said case law.
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You may want to also have a look here: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=LEGISSUM...
"According to the precedence principle, European law is superior to the national laws of Member States. The precedence principle applies to all European acts with a binding force. Therefore, Member States may not apply a national rule which contradicts to European law.
The precedence principle guarantees the superiority of European law over national laws. It is a fundamental principle of European law. As with the direct effect principle, it is not inscribed in the Treaties, but has been enshrined by the Court of Justice of the European Union (CJEU)."