WASHINGTON (Reuters) - Texas Attorney General Ken Paxton on Monday launched an investigation into Google's monopoly charges involving 50 prosecutors.

The investigation comes as Silicon Valley companies face growing scrutiny from the government over what critics see as monopolistic business practices.

The investigation will be bipartisan in support by prosecutors in 48 states, along with Washington, DC and Puerto Rico. The only states that did not participate in the investigation were California, where Google is based, and Alabama. According to Paxton, the group recently sent a request to Google for information.

"This is an investigation to determine the facts," Paxton told a news conference outside the Supreme Court building in the capital. "Currently it is about advertising, but the facts will lead to what they lead."

The press conference was held by a small group of prosecutors including Paxton, Karl Racine of Washington, Doug Peterson of Nebraska, and Eric Schmidt of Missouri.

Paxton explained that his office would be at the head of the team leading the investigation, which would meet for discussion every week, and each state would be allowed to intervene as much as it wants as the investigation would be "a very open process."

Missouri Attorney General Eric Schmidt speaks to Reuters after a press conference in which prosecutors announced the start of the investigation against Google (Reuters)

For now, the investigation will focus on Google's dominance of digital advertising, but prosecutors have also suggested the investigation could become broader and extend to other affiliates of Google's parent company, Alphabet. They mentioned smartphones and online video (YouTube).

Google is already under the microscope of regulators. Last Friday, the company said it had sent information about previous investigations on monopoly charges to the Justice Department. It also said it was preparing to answer similar questions from the state attorney general, ahead of Monday's announcement.

There has been recent news that federal regulators are clamping down on big tech companies, but a state-wide investigation could also mean a big headache for Google. In the past, prosecutors confronted the tobacco and mortgage industries, leading to their reform.