As per section 17 of IT act under perks you can find that it includes:
(v) any sum payable by the employer, whether directly or through a fund, other than a recognised provident fund or an approved superannuation fund 87[or a Deposit-linked Insurance Fund established under section 3G of the Coal Mines Provident Fund and Miscellaneous Provisions Act, 1948 (46 of 1948), or, as the case may be, section 6C of the Employees’ Provident Funds and Miscellaneous Provisions Act, 1952 (19 of 1952)], to effect an assurance on the life of the assessee or to effect a contract for an annuity;
So, any contribution other than recognized /approved PF fund will be taxable and any contribution in excess of 12%.