It is okay so far the PF qualifying wages is not less than Rs 15000. But it is always good if you take an undertaking from the employee that the reduction of PF contributing wages is as per their choice and understanding. There is no formal format for it but you can get it like..:
" I have been contributing to PF on my actual basic salary. But from this month onwards my contribution towards the EPF shall be limited to the statutory amount, ie, 12 percent of Rs 15000. I also accord permission to the employer to contribute his contribution at the same rate I contribute...."
This kind of undertaking may be useful in the future because in the future they should not say that their PF accumulation is less because their contribution was less. Moreover, if the EPFO or courts take a strategic decision that Pension shall be decided based on higher wages and PF contributions then the employees would blame you for not contributing on actual basic salary rather than on Rs 15000.