From previous experience, having to exclude communications from a single entity (or single type of entity) is not going to shut anything down. Case in point:

From previous experience, having to exclude communications from a single entity (or single type of entity) is not going to shut anything down. Case in point: It is unconstitutional to conduct surveillance on US citizens without a warrant. Therefore the NSA's massive collection machine must exclude every single American, right? Wrong. What they did instead was implement a filter where the accuracy of excluding a US citizen is greater than 50%. So if your exclusion rate is only 60% you "accidentally" catch 40% of US citizens in your surveillance net, but you have met the requirements. Similarly in this case if surveillance must exclude communications from a single law firm then they only have to implement a filter where they are more likely to exclude the communications than they are to catch them. "Accidentally" catching their communications would still be allowed since the filter would be meeting the requirements.