Apple executives are set to defend the company’s tax practices and call for corporate tax reform on Capitol Hill Tuesday amid harsh criticism following a Senate investigation.

A report released Monday by Senators John McCain, R-Arizona, and Carl Levin, D-Michigan, charged that Apple “has used a complex web of offshore entities — including three foreign subsidiaries the company claims are not tax resident in any nation — to avoid paying billions of dollars in U.S. income taxes.”

The report says Apple relies on a number of unusual accounting tactics along with a handful of subsidiaries in Ireland — where it has negotiated a tax rate of less than 2% — to reduce its tax bill. The U.S. corporate tax rate stands at 35%.

One Irish subsidiary, Apple Operations International (AOI),  has no employees or presence in Ireland, holding its board meetings and keeping its bank accounts in the U.S., the senators said. AOI reported $30 billion in income from 2009 to 2012, but its management structure allowed Apple to exploit a gap between U.S. and Irish law and avoid paying taxes in either country, the report claims.

In testimony posted online ahead of Tuesday’s hearing, Apple brushed off charges that it is gaming the U.S. tax system, saying it “pays an extraordinary amount in U.S. taxes” and “does not use tax gimmicks.”

The company disputed the characterisation of its subsidiaries as tax shelters, saying its Irish operations employ nearly 4,000 people and “are involved in manufacturing, distribution, technical support, sales support and finance support services.”

“For cash management purposes, these subsidiaries distribute foreign, post-tax income as dividends within Apple’s corporate structure,” Apple said. “Under US tax law, these foreign intercompany payments are not taxable.”

The cost-sharing agreement with its subsidiaries, Apple added, “is authorised by US law and complies with all US tax regulations.”

“This agreement allows the company to co-develop and share the risk of developing new products with its foreign subsidiaries,” Apple said.

Tuesday’s hearing comes amid criticism of American corporations over practices by which they lower their tax bills through legal means, holding cash overseas and funneling profits through subsidiaries in low-tax countries. Apple says this issue could be solved via new legislation, arguing that the U.S. tax system “has not kept pace with the advent of the digital age and the rapidly changing global economy.”

The California-based company holds more than $102 billion offshore, allowing it to avoid the 35% tax it would pay upon returning the money to the U.S. The firm recently borrowed $17 billion to buy its own stock from shareholders rather than draw on its overseas cash, avoiding substantial U.S. taxes as a result.