The SEC’s staff has recommended that the proposed acquisition of the Chicago Stock Exchange by Chinese investors be approved, setting the stage for a vote on a controversial deal that Donald Trump blasted on the campaign trail.

The Securities and Exchange Commission said Wednesday that its commissioners will decide in the coming weeks whether to allow the purchase, which is drawing increasing opposition from Congress. The acquisition, proposed in February 2016, cannot take place until the SEC approves it.

The stock market regulator declined to comment further, and it is unclear when it will ultimately rule on the fate of the deal.

The SEC’s unusual decision to weigh in on a stock exchange issue underscores the sensitivity of the deal and ensures it will draw even more attention. The Chicago Stock Exchange is the oldest in the U.S., dating back to 1882. But it is also one of the least-used trading venues in the country with less than 1 percent of the total daily stock trading volume.

Shortly after the proposed acquisition was announced, Trump railed against the deal as an example of the U.S. losing its competitiveness to China.

“China bought the Chicago Stock Exchange — China, a Chinese company,” Trump said in a nationally televised debate in South Carolina last year. “They are taking our jobs. They are taking our wealth. They are taking our base.”

Sen. Joe Manchin (D-W.V.), who is facing a tough reelection race in 2018, urged the SEC to reject the proposed acquisition in a July 20 letter to the agency.

“I fear that the challenges plaguing the Chinese market — lack of transparency, currency manipulation, etc. — will bleed into the Chicago Stock Exchange and adversely impact financial markets,” Manchin wrote.

In the House, Robert Pittenger (R-N.C.) has led a crusade against the exchange takeover by the Chinese.

The SEC staff decision to approve the CHX deal was expected by many. That’s largely because the Committee on Foreign Investment in the United States, a panel of government officials chaired by Treasury Secretary Steven Mnuchin, declined in December 2016 to block the deal, saying there were no unresolved national security concerns.

The new investor group will be led by Chongqing Casin Enterprise Group.

The Chicago Stock Exchange says U.S. investors would have a 50.5 percent stake in the exchange, while private Chinese investors would own 49.5 percent. Foreign investors will be required to submit to the jurisdiction of U.S. regulators and courts as well as provide open access to their own books and records, the exchange said.