The Internal Revenue Service on Wednesday proposed a rule aimed at ending a common and lucrative practice among private equity firms that allows them to artificially lower their partners’ personal income tax bills.

The practice targeted by the I.R.S. allows private equity firms to convert management fees they receive from their investors, which would normally be taxed as ordinary income, into capital contributions invested in their funds. Profits generated on such contributions are treated as capital gains or dividend income and subject to a sharply lower tax rate.

Converting a management fee to a capital contribution may be a “disguised payment for services,” the I.R.S. said in its proposed rule making, which it said was intended to provide guidance to partnerships and their overseers that such arrangements will be disallowed if they were done in such a way that no entrepreneurial risk was involved.

Private equity firms earn money from their investor clients in two ways. First is the management fee, which typically amounts to between 1 and 2 percent of the assets under management. Unless converted, such fees are taxed at ordinary income rates to the partners who receive them.