In February, 45 members of Congress signed a letter to the US Treasury Department's Committee on Foreign Investment (CFIUS), stating their concerns about a Chinese-led investor group's bid to buy the Chicago Stock Exchange.

But that's not the only deal on people's minds.

Sen. Sherrod Brown (D-Ohio) on Thursday wrote a letter to Treasury Secretary Jacob Lew highlighting national-security concerns surrounding a whole slew of announced deals.

Those included Syngenta's record-breaking $48 billion sale to ChemChina, Ingram Micro's $6.3 billion sale to HNA Group, GE's $5.4 billion sale of its appliance unit to Haier, and Terex's $4.9 billion sale to Zoomlion, in addition to the Chicago Stock Exchange deal.