connivance
secret approval
tacit consent

And such a claim might be based on the notion of "tacit consent".

It was a settled question, by tacit consent on both sides.

By remaining in society, one gives one's tacit consent to it.

The two, as by a tacit consent, drew back from the door.

The others did not even turn to look at him, he seemed to have done it by tacit unspoken consent.

For the next year, she will be forced to govern with the tacit consent of the military.

As though by tacit consent we had avoided any reference to the message.

I fail to understand the tacit public consent of the latter.

By tacit consent, they had adopted a plan of campaign.

"You know I cannot give even tacit consent to such a notion."