WASHINGTON (REUTERS) - A group of 46 US lawmakers urged regulators who investigate deals that could harm national security to take a hard look at a bid by a Chinese company to buy the storied Chicago Stock Exchange.

In a letter dated Tuesday (Feb 16), the lawmakers asked the Committee on Foreign Investment in the United States (CFIUS) to investigate plans by the Chongqing Casin Enterprise Group (CCEG) to buy the Chicago Stock Exchange, one of the oldest US exchanges. No terms were given for the deal, which was announced in early February.

"While it is unclear the level of influence the state holds over CCEG, the firm is involved in a number of important Chinese sectors that would likely require close ties to the state," the lawmakers said in the letter. "Additionally, the chairman of CCEG, Shengju Lu, holds a seat on an important industry committee overseen directly by the mayor of the Chongqing Municipality - implying a direct political connection," said the letter, which was sent to Marisa Lago, who takes a lead role at Treasury in the CFIUS.

The exchange, with locations in Chicago and New Jersey, is mainly used by market makers to buy and sell the most active exchange-traded funds and hedge their positions using futures on CME Group Inc's Chicago Mercantile Exchange. The Chicago exchange, which is known as CHX, is a niche player in the US equities market and executes about 0.5 per cent of US stock transactions.

The 46 signatories were all from the House of Representatives, and most were Republican. They included Rep. Robert Pittenger, a North Carolina Republican on the Financial Services Committee and the Congressional-Executive Commission on China. Pittenger cited concern that China, which has been accused of corporate espionage, would have access to the data of US companies who use the exchange.

He also noted that the US auditing watchdog Public Company Accounting Oversight Board (PCAOB), which fights fraud, has been frustrated with China.

"We need to be wary of the fact that they didn't pass a previous test with the PCAOB," he said.

Other signatories include Mike Coffman, a Colorado Republican on the House Armed Services Committee; Mike Conaway, a Texas Republican on the House Armed Services Committee and the Permanent Select Committee on Intelligence and Michael Fitzpatrick, a Pennsylvania Republican on the Committee on Financial Services.

CFIUS only rarely kills proposed mergers but several times a year it informally urges companies to scrap merger plans and they comply. Most recently, in January, Philips dropped a plan to sell an 80 per cent stake in its Lumileds division to Asian buyers because of pressure from CFIUS.

High-tech deals involving China appear to get the toughest scrutiny, although there are exceptions. CFIUS allowed International Business Machines Corp in 2014 to sell its low-end server business to Lenovo Group Ltd.