In general, illegal contracts are void.

一般来说，非法的合同是无效的。

youdao

The reason the mafia thrives in countries where it's hard to write legal contracts-- let's say some new parts of the former Soviet Union or some parts of Africa the reason the mafia thrives in those environments, is that it substitutes for the law and enforces both legal and illegal contracts.

黑恶势力在那些,书面协议不受保护国家不断壮大,比如前苏联新成员国 或者非洲,为什么黑恶势力在这些地方发展壮大,因为这是法律强制力的补充,它维系所有合同,不管是不是合法的

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Downing Street backed firms paying a living wage, but said restricting contracts in this way could be illegal.

BBC: Living wage: Ed Miliband pledge over government contracts

The government said it backed companies paying a living wage and would encourage more businesses to do so, but said restricting government contracts in this way could be illegal.

BBC: Derby City Council to introduce living wage from 2014