At long last, accounting regulators have published their final rule requiring public companies to expense stock options. The question is whether it will stand.

The Financial Accounting Standards Board announced its rule at a press conference Thursday. As expected, it won't take effect until June, and it did not prescribe a specific formula that companies must use to calculate their options costs.

On a conference call, FASB Chairman Robert Herz said the regulation, approved unanimously by the agency's seven-member board, will increase the transparency and comparability of financial statements.

"We believe it will provide investors and other users of financial statements with more complete, unbiased information," Herz said.

But whether companies will have to implement the new standard remains in doubt. Opponents of options expensing have mounted a

fierce campaign against the rule in Congress and at the

Securities and Exchange Commission

, both of which could override it. And some analysts believe that last month's election victory by Republicans could improve

the chance that policymakers will block options expensing.

Under existing rules, companies can choose how to value the options they hand out to their employees and executives, either by recognizing their intrinsic value or their fair value. Most have chosen to recognize the intrinsic value of those options. Since most options have a strike price that is equivalent to the market price of the company's shares, that intrinsic value is usually zero, meaning that companies effectively don't recognize any options expense.

But over the past several years, a growing number of companies have chosen to recognize the fair value of options. Using formulas such as the binomial method or the Black-Scholes model, companies calculate the long-term worth of each option they grant and then recognize the aggregate cost as a payroll expense on their income statements.

Current rules require companies that choose the intrinsic method to make a fair-value estimate of their options costs in the footnotes of their financial statements.

The new rule would eliminate the intrinsic method alternative. Instead, all companies would eventually have to recognize the fair-value cost of their options in their income statements.

Under the new rule, most public companies will have to recognize options costs beginning with their first quarterly or annual period that begins after June 15. Small public companies won't have to recognize options charges until their first quarterly or annual reporting period that begins after Dec. 15, 2005. And private companies won't have to start expensing options until their first fiscal year that begins after Dec. 15 of next year.

Though companies will no longer be able to choose whether to expense options, they will have some leeway in how to calculate their options costs. The new rule will allow companies to continue to use the Black-Scholes formula instead of the binomial method FASB initially favored.

Such formulas take into account variables such as the length of the option contract, the exercise price of the option and the expected volatility of the company's share price.

Some accounting watchdogs

have raised concerns that companies may -- or have already started to -- tweak those variables to try to bring down their estimated options costs. FASB officials said on the conference call that the proposed rule gives detailed guidance on how to correctly apply the new accounting standard.

Many investors, corporate guardians and accounting experts have been pushing for years to require companies to expensing stock options. Many of them have blamed the sharp rise in executive pay over the last 15 years on the increased use of options, which has been encouraged by the way they are accounted for.

FASB's new rule seeks to do what the agency failed to complete in the mid-1990s, when it last tried to require options expensing. Under pressure from Congress, FASB dropped the effort and crafted its current standard instead.

But the movement to force expensing gained strength after the recent Enron, WorldCom and other corporate scandals. Many governance experts attributed those fiascos -- at least in part -- to the use of options. Because options reward short-term movements in stocks, they encourage corporate managers to take short-sighted or even illegal steps to boost share prices, critics charged.

Additionally, expensing advocates assert that the current system allows companies to dramatically overstate their earnings by understating their true payroll costs.

In contrast, expensing opponents argue that current valuation formulas are wildly inaccurate and will lead to bogus charges and more confusing income statements. Among the most vocal opponents of expensing are

technology companies, which are among the heaviest employers of options.

Opponents also argue that expensing will force companies to abandon broad-based stock plans, which will affect employee morale and companies' productivity. Such expensing opponents have pressed Congress and the SEC to block FASB's rule before it takes effect.

That campaign reached a high point last summer when the House of Representatives

voted overwhelmingly to override FASB's then-prospective expensing rule. Since then, the measure to block expensing has been

bogged down in the Senate.

FASB previously planned to have companies start expensing options at the beginning of next year. But under pressure from the SEC, it

delayed the implementation of the rule. Some expensing watchdogs have worried that the delay will give the rule's opponents sufficient time to try to override it before it takes effect.