The Internal Revenue Service is backing away from proposals to more uniformly enforce a law that taxes personal use of employer-provided cellphones.

IRS Commissioner Doug Shulman on Tuesday asked Congress to repeal the 20-year-old law to ensure that neither companies nor workers will be subject to taxes for employees' personal use of work cellphones.

The request is a turnabout from last week, when the IRS proposed measures to improve enforcement of the law, which is now widely ignored by employers and employees. One option proposed by the IRS would have counted 25% of employee cellphone use as personal, and thus subject to tax as income.

"The passage of time, advances in technology and the nature of communication in the modern workplace have rendered this law obsolete," Mr. Shulman said.

He said the IRS proposals were aimed at clarifying a poorly understood law. "Some have incorrectly implied that the IRS is 'cracking down' on employee use of employer-provided cellphones. To the contrary, the IRS is attempting to simplify the rules and eliminate uncertainty for businesses and individuals," Mr. Shulman said.

IRS examiners have in the past couple of years challenged businesses and universities regarding personal use of employer-provided cellphones, in some cases leading to additional taxes being assessed.

"They are under a lot of heat to close the tax gap," said Abe Schneier , senior manager at the American Institute of Certified Professional Accountants, referring to taxes owed but not collected. "Maybe they thought they had come up with something that would gain a little revenue and at the same time simplify the paperwork," he added. "It didn't work out that way."

Under the 1989 law, the value of employer-provided cellphone services is taxable to the employee unless the person keeps detailed records showing the phone was used for work only.

The IRS hasn't withdrawn its proposals, and will still collect comment on ideas for how employers should account for personal calls.