With the April 15 deadline for federal income fast approaching, it’s a reasonable time to think about the tax code. Everyone agrees the federal income tax code is excessively complex, costing everyone from the individual filer to Fortune 500 companies billions of dollars worth of work to interpret and follow. There is debate about lowering rates while simplifying the code in ways that include eliminating or limiting many tax deductions, also known as loopholes.

That debate will wait for another day. But the expert use — some would say abuse — of corporate loopholes is a topic today.

The U.S. Senate subcommittee on investigations this week released a report saying that Caterpillar, the international manufacturer of earth-moving equipment, has avoided paying about $2.4 billion in U.S. income taxes over a decade by moving profits to Switzerland. The report says Caterpillar shifts an unreasonably large percentage of its income on the profitable spare parts business to Switzerland, where it pays a tax rate of about 4 percent — far below the stated U.S. corporate tax rate of 35 percent.

According to the report, Caterpillar paid $55 million to an accounting firm to devise a scheme to cut its U.S. tax bill. The report on the tax-avoidance effort notes that in the U.S., the company has about 4,900 workers, 54 manufacturing plants and 10 warehouses to support the global parts business. In Switzerland, where it’s paying the low tax, it has just 65 employees and no manufacturing or warehousing.

While the Caterpillar case is the most recent, the poster child for corporate tax avoidance is probably General Electric. In 2010, GE reported worldwide profits of $14.2 billion, with $5.1 billion of that coming from the U.S. Yet, its corporate tax bill that year was $0. Documents from 2009 reveal that over the previous five years its total profits were $26 billion and its tax payments to the U.S. Treasury were less than $0 — the company was issued refunds or tax benefits of $4.1 billion by the I.R.S.

The GE case has been in the news several times over the past several years and the company is known to have a tax department, including many former I.R.S. and Treasury officials, known for aggressive use of tax loopholes. Not only does the company extract maximum benefit from existing loopholes, but its army of lobbyists is considered among the most effective at having more loopholes added to the federal tax code to benefit GE.

When most people think of a corporate tax department, they assume the people working there concentrate on making sure the company complies with all tax laws. At GE, the tax department seems focused on finding angles and getting maximum benefit from loopholes. At GE, the tax department is a profit center.

Some of Silicon Valley’s most famous companies have come under fire for their aggressive use of tax laws and tax havens. Apple, Google, Microsoft and Amazon to varying degrees shift their European profits to low-tax Ireland. Apple Computer, according to a Senate investigation, paid just 2 percent tax on $74 billion in sales by using Ireland’s super-low tax rates, which were created to boost the country’s economy and create jobs.

These technology companies are known to have experts at writing computer code. Now, it’s clear they have experts at navigating every obscure loophole in the tax code.

Legal or not, there should be increased attention on legal tax avoidance by corporate America. Maybe there should be an Alternative Minimum Tax for companies, like there is for individuals. Big companies often complain that the U.S. has the highest stated corporate tax rate, but many pay much lower effective rates by using loopholes.

This avoidance has shifted more of the tax burden to individuals. In the 1950s and 60s, corporate taxes produced 30 percent of federal revenues. By 2009, that figure had fallen to 6.6 percent. It’s probably lower now.

With these big corporations companies going to such lengths to exploit tax loopholes, individual taxpayers are paying more than they should — and that’s unfair. Tax reform should focus on making the system simpler, more fair and returning to a balance of 70 percent from individuals and 30 percent from corporations, instead of 94 percent from individuals and 6 percent from corporations, as it is today.