What do you expect, it's China so you cannot expect First World employment laws.
Most FW countries now have strict regulations on this practise known variously by such titles as "Mondayising', 'Weekending' etc. It is very difficult to get over the regulatory barrier. One of the first problems is that government regulators and especially tax departments don't consider it a change of employment and require the new conditions of employment remain the same unless said department considers them an improvement (NOT the employers' view or even the employees' view of improvement).