The US Secretary of State Mike Pompeo has linked curtailing the spread of 5G telecommunications network by Huawei to the continuation of US intelligence sharing arrangements with partners and allies. Although no evidence has been supplied publicly, the expressed fear is that cyber security is at greater risk.
The Five Eyes is an expedient intelligence sharing arrangement, between a select group of governments. It derives from an exchange of letters. It is not a formal Treaty. By its very nature of course expediency is changeable should circumstances and context, change. Intelligence contributes to foreign policy, it does not make or define it.