If it is simply a screen to avoid applicants who would be massively unsuitable , membership of extreme political parties or heavily into drugs etc then perhaps not.
Otherwise you might need a form from HR for each social network you join.
The way I imagine this will play out in practice is that you will get companies who are "social reference agencies" or similar.
They will have special privileges with facebook etc and will be hired by other companies to screen applicant based on a number of factors and will produce a report for the client company that probably wouldn't contain any specific data etc but simply screen for any "red flags".
If it is simply a screen to avoid applicants who would be massively unsuitable , membership of extreme political parties or heavily into drugs etc then perhaps not.
Otherwise you might need a form from HR for each social network you join.
The way I imagine this will play out in practice is that you will get companies who are "social reference agencies" or similar.
They will have special privileges with facebook etc and will be hired by other companies to screen applicant based on a number of factors and will produce a report for the client company that probably wouldn't contain any specific data etc but simply screen for any "red flags".