26. Is there a ban on donors to political parties/candidates participating in public tender/procurement processes?

Financial resources may be transferred to a political party only by Polish citizens having permanent residence in the Republic of Poland, subject to the provisions of art. 24 paragraph 4 and 7, art. 28 paragraph 1 and provisions of laws regarding elections to the Sejm of the Republic of Poland and the Senate of the Republic of Poland and elections to the European Parliament in the field of subject subsidy.
Source: Article 25.1, Law on Political Parties,1997 (consolidated text 2018)

§ 1 The financial resources of the election committee of a political party can only come from the fund the election of the party, created pursuant to the provisions of the Act of 27 June 1997 on Political Parties

§  2  The  funding  coalition  election  committee  shall  only  come  from  election  funds  of  political  parties comprising the coalition election.

§ 3 Financial resources of:
1) the election committee of an organization,
2) the voters election committee
- shall only come from the contributions of Polish citizens with their permanent domicile in the Polish Republic, and bank loans taken out solely for purposes related to elections.

§ 4 The financial resources of the election committee for the candidate for President of the Republic can only come from the contributions of Polish citizens with permanent domicile in the Polish Republic, and the election funds of political parties and bank loans taken out for purposes related to elections.
Source: Article 132 § 1-4 , Election Code, 2011 (amended 2019)

Donors to political parties/candidates are not  restricted from participating in public tender/public procurement processes.

It is worth mentioning that corporate donations to political parties and to electoral committees are prohibited.