10. Is there a ban on donations from corporations with government contracts to candidates?

Código Electoral de la República de Panamá
Artículo 230: 
4. Los provenientes de empresas donde el Estado sea accionista. 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 230:
4. Those coming from companies in which the State is a shareholder.  5. Those coming from individuals or legal entities that directly or as part of an economic group, at the time of the donation are contractors of the State of public services.

Unofficial English translation.

There are two provisions: those coming from companies in which the State is a shareholder and those coming from individuals or legal entities that directly or as part of an economic group, at the time of the donation are contractors of the State of public services and those coming from companies in which the State is a shareholder.