The SEC blocked a proposed $20 million purchase of the 135-year-old Chicago Stock Exchange by a group of Chinese investors led by Chongqing Casin Enterprise Group. (Scott Olson/Getty Images)

The Securities and Exchange Commission on Thursday said lack of transparency was the reason it thwarted a controversial bid by a group of Chinese investors to purchase the 135-year-old Chicago Stock Exchange.

The decision comes during a period of heightened concern over China’s rise as a commercial power in the East and worries over its access to American intellectual property and U.S. citizens’ personal data.

FBI Director Christopher A. Wray gave voice to the fears during a Senate Intelligence Committee meeting on Feb. 13 when he said China was bent on surpassing the United States in superpower status and said Chinese spies were embedded in American academia.

The proposed Chicago Stock Exchange deal drew opposition from both sides of the political aisle, with foes saying it compromised U.S. financial markets.

“We saw this as a bad deal,” Rep. Robert Pittenger (R-N.C.) said Friday. “It had to be stopped. We felt that our economic security and trust in the marketplace were threatened.”

The SEC said in its 75-page decision that it did not know enough about the investors and was not confident it could properly monitor the privately owned exchange after the takeover.

“The inability of the Chicago Stock Exchange to obtain documents and information necessary for it and the [SEC] to resolve key questions regarding the funding of, and relationship between, upstream investors creates significant doubts about the Exchange’s ability to engage in this extensive monitoring,” the SEC said.

“Determining the ultimate owners is the key,” Pittenger said. “That was the problem.”

Some observers said that concern over national security did not fuel the SEC’s decision.

“This comes in context of the U.S. being worried about China as a rising national security threat,” said Derek Scissors, a China economist with the American Enterprise Institute. “Everyone will think this is part of that reaction. But it’s actually about transparency and inexperienced Chinese financial firms. This transaction is minor, and the Chicago Stock Exchange is small. This is not important.”

The Obama administration did not stand in the way of the proposed $20 million purchase of the Chicago Stock Exchange by a group of Chinese investors led by Chongqing Casin Enterprise Group.

The would-be buyer said it had no ties to the Chinese government. Supporters said it would spur Chinese business in U.S. markets.

President Trump publicly opposed the takeover during his campaign.

“They are taking our jobs. They are taking our wealth. They are taking our base,” Trump said during one speech.

Chongqing Casin could not be reached for comment. A spokesman for the Chicago Stock Exchange also could not be reached for comment.

The Chicago Stock Exchange announced the agreement to be acquired by Chongqing Casin in February 2016. Chongqin Casin invests in real estate and finance.

SEC staffers had approved the sale of the privately owned exchange last August, but SEC commissioners, led by Chairman Jay Clayton, overrode the staff recommendation and put the deal on hold. The proposed takeover had cleared the Committee on Foreign Investment in the United States (CFIUS), a panel that scrutinizes foreign investment for national security concerns.

The Chicago Stock Exchange was one of dozens of regional exchanges that started in the 1880s to help local companies sell their stock. It is one of the oldest still open.

But stock trading began to modernize and centralize toward the end of the 20th century, and the Chicago institution found itself marginalized. It now has less than 1 percent of the trading volume in the United States

“They are not a big player, they continue to not be a big player,” said Spencer Mindlin, an analyst who focuses on capital markets at the research and consulting firm Aite Group. “It’s an extremely competitive marketplace where size and scale really matter. They don’t have either.”

The Chicago Stock Exchange deal would have been a first for Chinese ownership of a U.S. exchange, but not the first time for a foreign company. Deutsche Börse bought the U.S.-based International Securities Exchange in 2007. Nasdaq then bought the exchange from Deutsche Börse in 2016.

Worries over Chinese ownership of U.S. properties is nothing new. The Chinese oil company CNOOC in 2005 withdrew its bid for California-based energy firm Unocal Corp. The decision came after U.S. politicians opposed the deal on national security grounds. Unocal was bought for $18.3 billion by California-based Chevron.

Last month, the U.S. government blocked the proposed $1.2 billion acquisition of the global payment services company MoneyGram by Ant Financial, an affiliate of the Chinese Alibaba Group.