A Chinese investor group's $22.0 million bid to acquire Chicago Stock Exchange Inc. may be in jeopardy as regulators again delayed a decision on the deal amid increased scrutiny from lawmakers.

Eighteen months after the transaction was announced, the exchange's future is in the hands of Securities and Exchange Commission as it prepares to make a final ruling on an undisclosed future date. On Aug. 9, the SEC overrode its staff's recommendation to approve the bid by "staying" the decision.

Chicago Stock Exchange is looking to the investor group, led by China-based Chongqing Casin Enterprise Group, to help grow its market share. It accounted for just 0.4% of U.S. equity trades executed in June, making it one of the nation's smallest stock exchanges, according to TABB Group data.

The planned deal comes as exchanges face an increased need for other revenue streams as profits from the historically dominant trading and clearing business have stagnated. The bid for Chicago Stock Exchange is another effort to pivot by the company, as it looks to establish itself in an increasingly fragmented trading space, said Spencer Mindlin, an analyst with Aite Group.

"[The Chicago Stock Exchange] may be running out of runway," he said in an interview. "If this deal falls through, I don't know if they can continue to stay afloat."

The exchange has previously pursued other ventures such as market data services to differentiate itself from its larger competitors, according to Mindlin. But with exchange operators like Intercontinental Exchange Inc. and Nasdaq Inc. developing market data products as key revenue drivers, the Chicago Stock Exchange is still looking for its specialization, he said.

With the still-pending deal, the exchange wants to become an initial public offerings hub for small and mid-sized companies, in addition to ongoing initiatives like a speed bump, which is pending regulatory approval.

The largest point of concern among the bid's critics surrounds the company's goal of making the exchange also a home for Chinese companies looking to go public, according to Holly Bell, a professor at the University of Alaska-Anchorage who studies market structure.

The tie-up has caused an uproar among federal lawmakers, who have put it in their crosshairs as President Donald Trump's administration pushes "anti-globalization rhetoric" and supports deregulation for Wall Street companies, Mindlin said.

Some on Capitol Hill have grown particularly wary about the Chinese government's role in China-based companies. "The line between the Chinese government and Chinese companies is generally indistinct," Bell said in an interview.

Several members of Congress have written to Trump, SEC officials and the Committee on Foreign Investment in the U.S. about national security concerns related to the possible deal. CFIUS approved the bid in December 2016.

"[China's] sustained efforts to steal intellectual property and state-sponsored cyber attacks present clear and present threats to our national security," Sen. Joe Manchin, D-W.Va., wrote in an Aug. 14 letter to Trump. "It is highly likely that they will employ similar deceitful practices to gain an unfair advantage in our financial markets through the acquisition."

Now, the group may be facing its toughest uphill battle yet as SEC Chairman Jay Clayton, a Trump appointee, and Commissioners Michael Piwowar and Kara Stein are set to rule on the deal's fate. The Aug. 9 delay could mean that at least one of the commissioners has "some serious concerns" about allowing Chinese investors access to market data and infrastructure, or plans to fast track Chinese companies' IPOs, Bell said.

"A longer delay means that [the deal's] less likely to get approved," she said. If the deal is blocked by the SEC, Bell said she believes the exchange will likely go out of business or be acquired at a lower price.

Chicago Stock Exchange in an Aug. 9 statement said it is "confident" the SEC commissioners will approve the deal. Anthony Saliba, an exchange board member, wrote that the deal has been wrongly criticized over its ties to Chinese investors in a January blog post. The acquiring group also contains U.S. investors.

But lawmakers' rhetoric has persisted in opposition to the possible deal.

"We've seen deals around the globe and the United States that represent more synergies [and] pose less risk that regulators and anti-trust regulators have said no to," Aite's Mindlin said. "I find it hard to believe that [the SEC will] allow it."

A Chicago Stock Exchange spokesperson declined to comment.