The Senate Finance Committee has decided that a little-known provision that would change tax rules on certain securities sales shouldn’t apply to mutual-fund firms. Even so, it would still apply to individual investors.

The provision would prevent investors from minimizing taxes, when they sell part of a position, by choosing the specific shares being sold. Instead, investors would have to sell their oldest shares first.

As first proposed, the change would have applied to fund companies as well as individuals.

But senators exempted fund firms after some of the largest ones, including Vanguard Group and Eaton Vance Corp., protested by saying the proposed change would tie their portfolio managers’ hands, make markets less efficient, and raise taxes on investors.

If the change is enacted for individual investors, “it will take tax planning out of the hands of investors and advisers, and it could make them less inclined to sell,” says Tim Steffen, director of advanced planning with Robert W. Baird & Co.