Last week, took effect in Iceland that aims to eliminate the persistent pay gap between men and women. But while Iceland's government has made a concerted effort to ensure pay equity, efforts have stalled in other developed nations, including the United States. Iceland's law stands out in a key way: Companies and organizations with at least 25 full-time employees must actually obtain government certification proving their pay policies are based on factors such as education, skills and performance, not gender. If not, they risk a fine of around $500 each day they are out of compliance. The demands made by America's laws aren't as rigorous, and that may be in part because the people making, enforcing and implementing the laws are still largely men, suggests Jill Gonzalez, an analyst at financial website WalletHub. "The pay gap still persists because women continue to have disproportionate representation in both corporate leadership positions, as well as political ones," she tells CNBC Make It. The Center for American Women and Politics reports that women make up less than 20 percent of the U.S. Congress. At the same time, Reuters notes, nearly 50 percent of Iceland's parliament, where the first-of-its-kind pay law was approved, is made up of women. The Equal Pay Act, first passed by Congress in 1963, mandated that men and women be given equal pay for equal work, and, some states, like Minnesota, have equal-salary policies. But legislation in America has not been very effective: Women, on average, are still paid 20 percent less than men.

A recent report from the Pew Research Center, conducted before 2017's wave of , notes that employed women are five times more likely than employed men to say they've earned less for doing the same job. Even education level doesn't reduce pay disparity much, according to Pew data. Working women with a bachelor's degree or higher level of education were more likely than those with less education to say they've earned less than a man who performed the same job. The same is true for women with higher incomes: 30 percent of women with family incomes of $100,000 or more report they've earned less than a man who was doing comparable work, Pew notes, compared with roughly one-in-five women with lower incomes. In popular, high-paying , women are offered lower starting salaries than their male counterparts for the same job at the same company 63 percent of the time.

The pay gap still persists because women continue to have disproportionate representation in both corporate leadership positions, as well as political ones. Jill Gonzalez WalletHub analyst

Reasons for the disparities could include an "unconscious bias during the interview process that determine a candidate's salary based on what he or she was previously making, rather than the market rate for that individual's skills and years of experience," one study notes. Susan Vitale, chief marketing officer at tech company iCIMS, agrees. "Past inequality begets future inequality," she tells CNBC Make It, citing the company's Women in the Workforce report. "It's extremely common for employers to ask candidates their salary history instead of, or in addition to, their salary expectations or requirements. "If women were previously underpaid," she says, "sharing their salary history may impact a future offer, compounding the issue." While this practice was , "women have been adversely affected by the question for years." Some experts predict women in the United States won't reach pay equity with men until 2119. That would be about 150 years after the passage of the first Equal Pay Act.