In what could be an unintended consequence, the sales tax hike set for next April may tempt companies to replace their regular workers with "haken" temporary workers, some tax law experts say.

This could mean the ranks of the nation's nonregular workers, which have grown in recent decades and now make up a third of the workforce, could swell further. As of 2010, the number of temporary workers dispatched by employment agencies stood at 2.71 million.

Under the consumption tax law, companies are currently allowed to deduct the 5 percent tax from the costs of goods and services they buy from suppliers, which include payments to temp agencies, because theoretically the costs include the tax.