Congress is putting the Obama administration on notice that it has strict expectations for a nuclear agreement with Iran as the July 20 deadline fast approaches.

Some 344 House members — almost 80% of the lower chamber — signed a letter to President Obama on Thursday, telling him he would be "wise" to listen to what lawmakers have to say if he wants them to lift sanctions on Iran as part of a nuclear deal. Meanwhile, in the Senate, two hard-liners filed legislation to slap sanctions on President Hassan Rouhani and the supreme leader, Ayatollah Ali Khamenei, in what's likely to be one of several Iran bills introduced in the next few weeks.

The burst of activity comes as negotiators appeared ready to ask for an extension because they remain too far apart to quickly reach a deal, Al-Monitor's Laura Rozen reported Wednesday. A delay is politically risky, however, as keeping Congress at bay will become increasingly difficult as the midterm elections approach and Republicans seek to hit the Obama administration on national security.

"So far they've been able to rope-a-dope us on" new sanctions, said Sen. Marco Rubio, R-Fla., the co-sponsor of the human rights bill and a potential 2016 presidential contender. "But I hope there will be [renewed attention to Iran], and I think that will only be heightened if [the US and its international negotiating partners] fail to reach a satisfactory agreement, as I expect they will."