Facebook (FB) and Amazon (AMZN) have been spending big to influence government policy on Capitol Hill. Each company has spent around $4 million on lobbying in the second quarter of 2019.

Another tech giant, Google (GOOGL), spent much less, at $2.9 million for the quarter. Apple (APPL) was the lowest spender in the pack, at $1.8 million for the second quarter.

These four tech companies are currently embroiled in an antitrust investigation which began at the beginning of June. The investigation aims to find out whether these companies have too much influence over the market and whether they have been violating antitrust law.

House Judiciary Chairman Jerrod Nadler, D-N.Y., has said that "there is growing evidence that a growing handful of gatekeepers have come to capture control over key arteries of online commerce, content and communications."

Democratic presidential candidates have also taken aim at the big tech companies, with Massachusetts Sen. Elizabeth Warren vowing to "break up big tech" and introduce legislation if elected president that would set new antitrust standards for the companies.

Some of these companies have influence over major players on Capitol Hill. Senate Minority Leader Chuck Schumer, D-N.Y., has defended Facebook from criticism in the past. Schumer's daughter works at the company and he has received contributions from the social media giant.

Antitrust investigations are also being opened against big tech companies internationally. Amazon, the leader in the e-commerce industry, is being investigated by European authorities to see if the company is using sales data to get unfair leverage over its competition.

"E-commerce has boosted retail competition and brought more choice and better prices," EU Competition Commissioner Margrethe Vestager said last week.

"We need to ensure that large online platforms don't eliminate these benefits through anti-competitive behavior. I have therefore decided to take a very close look at Amazon's business practices and its dual role as marketplace and retailer, to assess its compliance with EU competition rules."

FAANG — the acronym for Facebook, Amazon, Apple, Netflix (NFLX) and Google (now Alphabet, Inc.) — have generated much attention from Wall Street, prompting concerns that their growth is hurting smaller companies.

Amazon has dominated online retail and has seen growth from its video streaming service. Facebook operates not only its social platform but also Instagram and WhatsApp services. Google is the most used online search engine and offers other web services. Apple is the leader in consumer electronics.