BOSTON (AP) — Tax privacy laws make it impossible for state auditors to determine whether the billions of dollars given out to private companies in the form of tax breaks are really worth it, Massachusetts Auditor Suzanne Bump said Tuesday.

Bump asked lawmakers to approve a bill that would provide her office with access to corporate tax returns filed with the state revenue department.

In prepared remarks before the Legislature's State Administration and Regulatory Oversight committee, Bump said such information is vital determine if the companies are eligible for the tax breaks and "to measure the effectiveness of tax credits in accomplishing their intended results."

In 2011, Bump analyzed 92 business tax breaks — officially known as tax expenditures — totaling more than $2 billion each year and found that most lacked sunset clauses — automatic reviews after a fixed period of time — or so-called "clawback" provisions that allow the state to recoup some of the lost revenue if a company that receives an incentive fails to meet job creation goals or other benchmarks.

Bump said her office was now trying to go a step further by determining if the tax incentive program itself is effective, but was frustrated by confidentiality rules that prevented access to tax returns filed with the revenue department.

She said 36 other states give their auditors the power to review tax returns.

Business leaders have raised objections to giving the auditor — an elected state official — the ability to review and possibly make public sensitive information contained in corporate tax returns. Bump on Tuesday sought to reassure businesses that the purpose of her review would be only to assess whether the tax breaks were good public policy, and not to target any individual companies.

"The bill before you ... is crafted more narrowly than in other states in that it is restricted only to tax return information that is necessary to audit tax expenditures," she said.

There was no immediate indication of when the committee might act on the legislation.