NEW YORK (AP) — Twenty-six big U.S. companies paid their CEOs more last year than they paid the federal government in tax, according to a study released Thursday by a liberal-leaning think tank.

The study, by the Institute for Policy Studies, said the companies, including AT&T, Boeing and Citigroup, paid their CEOs an average of $20.4 million last year while paying little or no federal tax on ample profits, according to regulatory filings.

On average, the 26 companies generated net income of more than $1 billion in the U.S., the study said.

The study blasted tax rules allowing unlimited deductions for CEO "performance-based" pay, like many stock options. It said the five biggest performance payers among the 26 companies took $232 million of these deductions last year.

Among the "kingpins" it criticized was CEO James McNerney Jr. of Boeing. It said he got $18.4 million in pay last year while his company received a tax refund of $605 million.

The study also laid into Citigroup for paying CEO Vikram Pandit $14.9 million while the bank received a net $144 million in tax benefits.

Eighteen of the 26 companies received cash back or credits to apply against tax in the future, according to the report.

The study, a 45-page attack on the corporate tax code, said deductions and credits are allowing companies to lavish big pay packages on executives so they can cut their tax bills while Washington gets less money in a time of trillion-plus deficits.

"Our nation's tax code has become a powerful enabler of bloated CEO pay," the study said.

To calculate tax, the study used companies' own math based on accounting rules. Regulators require companies to estimate their tax bill and disclose it in public documents for investors.

The tax filings the companies make to the government, typically in September, are private and can differ from the estimate.

Another problem is that the study doesn't count tax the company plans to pay but has deferred to future years. The authors argue that deferred tax can be put off indefinitely.

Charles Bickers, a Boeing spokesman, said that the company's federal tax bill, including deferred tax, was $1.3 billion last year, not a net credit, as the think tank's study found.

Boeing did lower its tax, in part by using a popular tax credit encouraging companies to spend more on research and development. Bickers said that helped the company hire 11,000 people in the U.S. last year.

"Boeing supports a simpler, more competitive tax code. At the same time, we have put the R&D tax credit to exactly the use it was designed — creating U.S. jobs in a high-value, advanced technology industry," he said in a statement.

The Institute for Policy Studies said Boeing would have spent the money on R&D without the credit.

In addition to performance-pay deductions and R&D credits, the report criticized the use of tax havens that allow technology companies, for instance, to assign intellectual-property rights to shell companies in the Cayman Islands, so they can run profits through them and avoid taxes. It noted that 26 companies have a combined 537 subsidiaries in tax-haven countries.

The study also cited accelerated depreciation on investments, which allows a company to take deductions for big-ticket purchases in one year, as opposed to over several years. That cuts taxes in the first year.

The study said AT&T used accelerated depreciation to save $5.2 billion on its 2011 taxes while paying CEO Randall Stephenson $18.7 million last year.

Sarah Lubman, an AT&T spokeswoman, said the point of accelerated depreciation is to encourage companies to make investments. She said AT&T made $20 billion in investments last year, helping to "drive the economy and support good-paying jobs."

She also said that the deductions won't be available to take in future years, which should increase taxes.

A Citigroup spokeswoman noted that the company lost money in 2008 and 2009 and used the losses to offset taxes on profits this year.