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

Código electoral de la República de Panamá
Artículo 145: 
Fuentes prohibidas de recaudación de fondos. Quedan prohibidas las siguientes donaciones o aportes a partidos políticos, precandidatos y candidatos:
(...) 5. Los provenientes de personas naturales o jurídicas, que de forma directa o como parte de un grupo económico, que, al momento de la donación, sean contratistas del Estado o concesionarios de servicios públicos.

Article 145. Prohibited Sources of Fundraising. 
The following donations or contributions to political parties, precandidates, and candidates are prohibited:
(...) 5. Those from natural or legal persons who, directly or as part of an economic group, at the time of the donation, are contractors of the State or concessionaires of public services.

Unofficial English translation.

There are provisions that prohibit individuals or entities who are contractors or concessionaires of the State from making donations to political parties or candidates.