Under a set of long-awaited proposed regulations issued Wednesday, the U.S. Internal Revenue Service (IRS) said it would allow some natural gas and oil industry fracturing (fracking) services to be qualified for favorable tax treatment under master limited partnerships (MLP).

The exploration and production industry had been relying on private letter rulings (PLR) from the IRS to determine whether such activity generated qualified income, but the IRS halted the process in March 2014 until it could develop and issue the proposed rules.

Under the IRS’ MLP rules, 90% of a business’ gross income must be from qualifying income in order to be taxed as a partnership.

In its proposal, the IRS clarified that fracking services must be “intrinsic” to the exploration, development, mining or production, processing, refining, transportation or marketing of minerals or natural resources, according to a Wednesday Federal Register notice.

An activity would qualify as an intrinsic activity only if it is specialized to support operations, is essential to its completion and requires the provision of significant services, the IRS said. Simply providing equipment or other goods would not result in qualified income, for instance.

Comments are due to the IRS by Aug. 4.