NEW YORK (Reuters) - MSCI Inc on Tuesday said it is looking into the possibility that Facebook Inc user data was accessed by the consultancy Cambridge Analytica.

The stock index provider currently rates Facebook as "average" in its environmental, social and corporate governance, or ESG, data, which is used as a template by funds and investors that aim to buy companies with a positive social impact. A spokeswoman said MSCI cannot yet share any impact the review could have on Facebook's ESG rating.

The social media company is not currently seen as a high performer on ESG issues relative to its industry peers, MSCI said.

An increasingly vocal base of investors who put their money where their values are have raised concerns about Facebook and are reassessing whether they should own one of the market's tech darlings. More than $20 trillion globally is allocated toward "responsible" investment strategies in 2016, a figure that grew by a quarter from just two years earlier, according to Global Sustainable Investment Alliance, an advocacy group.

Facebook shares sank about 12 percent over the two trading days this week as investors worried that potential legislation could damage the company's advertising business. Facebook Chief Executive Mark Zuckerberg is facing calls from lawmakers to explain how the political consultancy hired by Donald Trump's election campaign reportedly gained improper access to data on 50 million Facebook users.

Cambridge Analytica has strongly denied the media claims and said it deleted all Facebook data it obtained from a third-party application in 2014 after learning the information did not adhere to data protection rules.

Facebook said on Monday it had hired digital forensics firm Stroz Friedberg to carry out a comprehensive audit of Cambridge Analytica and that the company had agreed to comply and give the forensics firm complete access to its servers and systems.

(Reporting by Trevor Hunnicutt; Editing by Susan Thomas and Dan Grebler)

By Trevor Hunnicutt

Stocks treated in this article : Msci Inc, Facebook