Here is an interesting article (the Illegality of Advocating for Jury Nullification) written by two lawyers who suppport the federal government's effort to prosecute Professor Heicklen for jury tampering. According to the authors of the article, Professor Heicklen crossed the line when he stood outside the federal courthouse in New York and handed out pamphlets with the following language:
The judge will instruct the jury that it must uphold the law as he gives it. He will be lying. The jury must judge the law as well as the facts.
Juries were instituted to protect citizens from the tyranny of the government. It is not the duty of the jury to uphold the law. It is the jury's duty to see that justice is done....
Once on a jury, must I use the law as given by the judge, even if I think it's a bad law, or wrongly applied?
The answer is "No. You are free to vote on the verdict according to your conscience."