There are two parts of Title 17 which relate to position limits: Part 150 (Limits on Positions) and Part 151 (Position Limits for Futures and Swaps). This page is about the latter; for details of the former see the dedicated Part 150 page.
On 18 November 2011 the CFTC published details of the addition of Part 151, alongside a change to Part 150, in the Federal Register (see 77 FR 71684). The new and amended rules were due to become effective on 12 October 2012.
The new rulemaking was an attempt by the CFTC to, amongst other things:
Following a legal challenge by the International Swaps and Derivatives Association (ISDA) and the Securities Industry and Financial Markets Association (SIFMA), the U.S. District Court for the District of Columbia vacated the rulemaking, with the exception of the amendment to 17 CFR §150.2.
As a result, Part 151 is null and avoid.