The European Commission recently fined Amazon (NASDAQ: AMZN) 250 million euros ($294 million) to cover unpaid back taxes plus interest. The EU alleges that Luxembourg's government illegally allowed Amazon to set up subsidiaries that were designed to minimize its taxes.

Most of Amazon's European profits are sent to Luxembourg-based subsidiary Amazon EU SARL. That subsidiary pays royalties to another Amazon subsidiary, Amazon Europe Holding Technologies, which is exempt from corporate taxes. The commission claimed that Amazon intentionally inflated those royalties to reduce taxes on Amazon EU SARL.

EU Commissioner for Competition Margrethe Vestager said in a press release that the setup enabled Luxembourg to give "illegal tax benefits" to Amazon, which allowed it to pay "four times less tax than other local companies subject to the same national tax rules."

As a result, Amazon was asked to pay eight years of back taxes plus interest. The commission says that the payment isn't a fine, preferring to call it a recovery of taxes. Amazon said it might appeal the ruling, even though $300 million would represent only 0.2% of its projected revenues this year.

Another red flag for tech companies

While the financial impact to Amazon should be minimal, the case is another clear indicator that the EU is cracking down on tax-minimizing setups and anticompetitive deals across the region.

Last August, Apple (NASDAQ: AAPL) was ordered to pay a record 13 billion euros ($15 billion) in back taxes. The commission claimed that Apple received illegal tax breaks in Ireland that reduced its effective corporate tax rate of 1% on its European profits to 0.005% between 2003 and 2014.

In May, the EU fined Facebook (NASDAQ: FB) $122 million, claiming that it provided misleading information during its 2014 acquisition of WhatsApp. Facebook initially stated that it wouldn't link Facebook and WhatsApp accounts, but it allegedly broke that promise last year when it started sharing data between the two platforms.

In June, the EU fined Alphabet's (NASDAQ: GOOG) (NASDAQ: GOOGL) Google 2.4 billion euros ($2.8 billion) for promoting its own shopping service over other e-tailers. The commission is also probing Google's Android and AdSense, claiming that the platforms enable the company to dominate internet-based searches and ads.

Looking ahead, Microsoft (NASDAQ: MSFT) -- which sends its overseas profits through subsidiaries in Luxembourg, Ireland, and other low-tax countries -- could be next on the European Commission's list.