9. Is there a ban on donations from corporations with government contracts to political parties?

Source: 
公職選挙法, 1950 (2022改正)
Public Offices Election Act, 1950 (as amended by Act No.68 of 2022)

第百九十九条 衆議院議員及び参議院議員の選挙に関しては国と、地方公共団体の議会の議員及び長の選挙に関しては当該地方公共団体と、請負その他特別の利益を伴う契約の当事者である者は、当該選挙に関し、寄附をしてはならない。

第二百条　２　何人も、選挙に関し、第百九十九条に規定する者から寄附を受けてはならない。

Article 199 Persons who are parties to contracts with national or local governments involving special benefits shall not make donations in connection with elections for members of the House of Representatives and the House of Councillors, or for members of the assemblies and heads of local governments.

Article 200. 2. No person shall accept donations from persons prescribed in Article 199 in connection with an election.

A person with government contracts shall not contribute political funds in relation to an election. This ban applies to both candidates and parties. There is no provision that bans a person with government contracts from contributing political funds not in relation to an election.