With Congress back in session, two US senators are planning to propose a new round of sanctions on Iran. The sanctions, the collective brainchild of Sens. Mark Kirk (R-Ill) and Robert Menendez (D-N.J.) would  “restrict nearly all forms of international trade and transactions,” moving closer to an effective total embargo on Iran.

But at this crucial stage, new and tougher sanctions may actually undermine the prospects for a negotiated solution to Iranian nuclear aspirations.

The new sanctions would expand existing restrictions on Iran, widening the net of current sanctions to include not only Iran’s oil markets, but also agricultural, industrial, and consumer goods. In this way, they would get at the heart of the “basic functioning of [Iran’s] economy.”  The new measures would also demand that foreign countries freeze Iran’s access to its overseas currency reserves. Kirk and Menendez are working on this proposal amidst widespread agreement that the administration’s existing sanctions are having the desired economic effect – something that even Israel’s foreign ministry has acknowledged.

So do we need a new round of sanctions right now? To answer that question, it’s important to keep the end goal in mind: the intention of any sanctions against Iran is to persuade the regime to accept international limits on its nuclear program. And there are already some indications that  Iran is inching toward more productive negotiations with the P5+1 on this matter.

Our friends at the National Security Network reported on November 13 a number of promising signs that Iranian officials are not only ready to start a new round of negotiations, but they’re in fact willing to consider direct bilateral talks with the U.S., a negotiation format that has long eluded both sides, and that analysts agree have a greater chance of success.

With existing multilateral sanctions apparently having the desired effect, and Iran quite possibly on the verge of taking crucial steps toward negotiations, it is precisely the wrong time to impose new sanctions. What makes sanctions effective at the negotiating table is the prospect of having them lifted, which theoretically gives Iran an incentive to agree to what we’re asking for in return. As Iran expert Trita Parsi put it back in January: “… right before [sanctions’] imposition — at the moment where they remain a withdrawable threat — their effectiveness is at their height.”

Therefore, Iran needs to be confident that the easing of sanctions is a real possibility, in order for any talks to be effective. But if we go through the process of debating, passing, and implementing a new and more draconian round of sanctions, Iran is likely to receive the opposite message – that we have no intention of making concessions, and that we seek not a deal, but outright regime change.

Like trouble, a sanctions regime is much easier to get into than to get out of. In particular, U.S.-specific sanctions are difficult to reverse, because they require an act of Congress rather than a decision by the President. Moreover, as anyone familiar with the U.S. legislative process knows, a new round of sanctions will require a significant investment of energy, time, and resources, one that lawmakers and administration officials will be reluctant to unravel once the sanctions go into effect.

This wouldn’t be the first time that the chance for progress with Iran has been derailed by a “runaway train” of sanctions policy, driven by  overzealous advocates. Parsi believes that, in May 2010, Washington was unable to accept a promising nuclear deal with Iran – the “fuel swap” agreement brokered by Turkey and Brazil –  because the United States  had just negotiated a tough new round of sanctions, making its commitment to the sanctions policy “irreversible.”

Now, as before, policymakers intent on tightening sanctions are forgetting that there’s a next step: to demonstrate that, as part of a negotiated deal, we’ll indeed be willing to lift those sanctions. As author Christopher de Bellaigue warned in a recent piece in The New Republic, “the danger is that sanctions will have ceased to serve as an instrument of policy, and simply become the policy itself.”

Similarly, Gary Sick, who worked on Iranian affairs in the White House during the Iranian revolution and the hostage crisis, worried in a CNN op-ed that “[s]anctions have assumed a life of their own and are gradually becoming politically untouchable.”

The Obama administration has pursued a sanctions policy with broad international support that has put enormous pressure on Iran.  But by adding to this pressure, the United States risks becoming further committed to a policy of more and more sanctions, while making it difficult to attain its ultimate goal:  a mutually acceptable diplomatic solution.