It appears that they can ask you to do it
Here is some information.
They will not grant you spanish citizenship unless you sign that you have renounced your Australian citizenship.
I understand that many people lie about it.
But renouncing your australian citizenship will result in you having to get a visa here to stay.
Also unless you hold citizenship of another country they will not let you renounce it.
So you will not be granted spanish citizenship unless you sign you have renounced the australian one.
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