Usually disclose and recuse. You’re conflicted, so you shouldn’t make the decision or be involved in making the decision, but if it’s the best vendor for the company the company isn’t prohibited from using their services. Most large companies will have a policy for declaring and managing that type of conflict.

In addition to generic criminal laws against fraud and bribery there’s also honest services fraud (which I’ve mentioned elsewhere in this thread) which boils down to depriving someone to whom you owe a duty of the right to your honest services.