WASHINGTON – The nation’s tax law is so thick and complicated that businesses and individuals spend more than 6 billion hours a year complying with filing requirements. That’s the equivalent of 3 million people working full-time, year-round.

As a result, about 90 percent of filers will either pay a tax preparer or use a computer software service to help with their federal tax returns this spring, according to a report Wednesday by an independent government watchdog.

“The existing tax code makes compliance difficult, requiring taxpayers to devote excessive time to preparing and filing their returns,” said the report by Nina E. Olson, the National Taxpayer Advocate. “It obscures comprehension, leaving many taxpayers unaware how their taxes are computed and what rate of tax they pay. It facilitates tax avoidance by enabling sophisticated taxpayers to reduce their tax liabilities and provides criminals with opportunities to commit tax fraud.”