Lawmakers need to overhaul the tax code completely to reduce the ‘‘significant, even unconscionable, burden’’ placed on taxpayers just to file a tax return, the Internal Revenue Service’s ombudsman told Congress on Wednesday.

In her legally required annual report to Congress, the national taxpayer advocate, Nina E. Olson, estimated that individuals and businesses spend about 6.1 billion hours a year complying with tax-filing requirements. That adds up to the equivalent of more than 3 million full-time workers, or more than the number of jobs on the entire federal government’s payroll.