I haven't had a look at the detail for some time but essentially it is legislation that requires employers to offer all employees a choice as to where they pay their employer contributions into super - that is the 9% compulsory super contribution that employers pay.
In the past, the employer was able to direct the employee to open an account with the employers preferred provider and contributions were then paid into that account. It was one of the major causes of multiple super / lost super accounts.
From the employers view, it was easier and administratively cheaper to have just one or two companies into which they had to pay super on behalf of employees. There will be difficulties and I believe there are a number of exemptions although I don't know the details of these.
I seem to recall that the original proposal required the employer to offer a minimum of four choices and at least one of these had to be a company of the employees choice.
