I am pretty sure we covered this before but the message is not getting out. If someone puts your site in their disavow link file, it will NOT have a negative impact on your rankings.
There are many link spammers trying to get their links removed from sites and are using very threatening emails and messages to encourage those sites to remove the links. One example is in a thread at Google Webmaster Help.
Here is part of the message:
We would like to bring your notice that failure to remove these links would require us to file a "Disavow Links" report with Google. Once we submit this report to Google, they may "flag" your site as"spammy" or otherwise if anything is not in compliance with their guidelines. The last thing we want is to have another web master go through this grief!
John Mueller from Google responds to the concern saying:
They are wrong. Having URLs from your website submitted in their disavow file will not cause any problems for your website. One might assume that they are just trying to pressure you. If the comment links they pointed to you are comment-spam that was left by them (or by someone working in their name) on your website, perhaps they are willing to help cover the work involved in cleaning their spam up?
I love how he outright calls them wrong and then goes on and suggests they pay up to remove the link they placed on their site. It is like throwing it back in their face and using a tactic the spammer would have used.
Forum discussion at Google Webmaster Help.
