Several Democrats in the U.S. House of Representatives joined Republican colleagues last week in supporting setting conditions before Boeing can proceed with a $17.6 billion deal to sell 80 passenger aircraft to Iran Air.

The United States Treasury Department says it has the tools to ensure the aircraft won’t be diverted to unapproved purposes, but a bipartisan cadre of legislators want Iran to meet certain criteria before the administration approves the sale.

“We’re being asked to transfer planes to a company, Iran Air, that has served as an air force for terrorism,” said Rep. Brad Sherman (D-California) at a hearing of the House Financial Services Committee’s trade subcommittee. “And we’re being told, oh, but just trust them, or just trust that we’ll be able to do something if they violate. When Iran comes forward with a plan to guarantee that these planes are not being used for terrorism or to support [Syria’s] Assad, then we could consider” granting export licenses.”

Sherman opposed the nuclear deal made the Boeing sale possible. Several supporters of the Iran nuclear agreement also raised caveats.

“What kind of things would you expect to see in the license to make sure that planes are not available for any kind of illicit or illegal activities under the agreement or any other sanctions legislation?” asked Rep. Ed Perlmutter, D-Colorado of the panel of witnesses at the congressional hearing.

The top Democrat on the subcommittee, Rep. Gwen Moore of Wisconsin, suggested that lawmakers might want to “tighten up on the licensing.”

The Obama administration said the airplane sale would create goodwill in Iran by helping to modernize the country’s airline sector. But skeptics note that Iran Air is still flying arms to President Bashar al-Assad of Syria, who is fighting a civil war, on behalf of the Islamic Revolutionary Guard Corps.

Republicans were happy to hurl “I told you sos” the Democrats way. Subcommittee chair Bill Huizenga, R-Michigan was quoted as saying that the Democrats “now want to start adding provisions.”

Republicans have proposed legislation which would absolutely prohibit any aircraft sale to Iran, arguably a violation of the nuclear deal as long as Iran remains in compliance.

The July 7 hearing could also have laid the groundwork for potential bipartisan compromise. The nuclear deal allows “the sale of commercial passenger aircraft and related parts and services to Iran,” but also prohibits their use “for purposes other than exclusively civil aviation.”

One observer noted that this provision would allow Congress to legislate an interim period during which Iran could extricate its airlines from prohibited activities before aircraft sales go through.