In less than 24 hours, California’s Fair Pay Act will take effect. The new law, passed this October with unanimous bipartisan support in the California state senate, has been called the “strictest” fair-pay law in the U.S., and it applies to any company that has an office in the state.

Under the Fair Pay Act, Californian companies are now required to justify pay differences between male and female employees doing “substantially similar” work regardless of job title. (Prior fair pay legislation only required men and women of the same job title to be paid equally.) This effort to close the gender pay gap—women on average make 84 cents for every dollar men make in California—also includes language that legally guarantees employees the right to ask coworkers about pay without retribution from management.

The Wall Street Journal reports that some Californian companies have, in advance of the law, been reassessing the way they pay their employees, but are finding that isn’t as easy as it sounds. Pay audits are often based on information from the human-resources department (such as job title and job description), which might not be sufficient in evaluating whether two jobs are really the same; going to employees to answer these questions can be time-consuming.