Media Matters Vs. Fox-Non-Profit Group?

As Media Matters prepares it's 'war' on Fox News, the issue of how far non-profit groups can go politically is being discussed.

As the Hilary Clinton founded, George Soros funded Media Matters announced it is waging a 'war' on Fox News, the issue has been raised as to whether it's violating it's Federal status as a 501(C3) group.  Such groups are classified by the IRS as non-profit, educational-informational foundations, who are expressly forbidden from engaging in lobbying, or other political activities.   There is no evidence, or MM has not released it yet, that they plan to ask the IRS to change their 501 status.   Should they openly launch an effort to "discredit" Fox News, or any other media outlet, politicial organization or candidate on either side of the fence, then based upon IRS code they would be in violation.   However, some say MM has been engaged in such activities 'behind the scenes' for years; it's only now they are openly stating their intentions.