President Barack Obama’s efforts to thwart new sanctions against Iran seem to have worked. A group of 10 Senate Democrats said on Tuesday they wouldn’t vote for new sanctions against Iran on the Senate floor until late March, according to The Wall Street Journal.

In a letter to Obama, Sens. Robert Menendez (D., N.J.), Charles Schumer (D., N.Y.) and eight of their colleagues said they are skeptical that Iranian negotiators will make the concessions necessary to ensure the framework for a deal with global powers comes together by a March 24 deadline for a political deal, ahead of a end-of-June agreement containing technical details.

Calling the deadline a “crucial test of Iranian intentions,” the senators said they would not back legislation, written in part by Menendez, until that time.

“Considering Iran’s history in nuclear negotiations and after two extensions… we are concerned that Iran is intentionally extending the negotiations to improve its leverage at the negotiating table,” the senators wrote to the White House, according to The Wall Street Journal.

Menendez, a longtime proponent of additional sanctions against Iran, has introduced legislation that would mandate new sanctions only if a nuclear deal is not reached by March, a timetable that has already been extended past the original November deadline.

The bill co-authored by Menendez and Republican Senator Mark Kirk is a toned down version of a previous bill they authored and which had gained momentum in Congress, but Obama lobbied hard against it and threatened to veto it.

Last week, even after Obama used his State of the Union address to argue against new sanctions, Menendez pushed for sanctions again, saying the Islamic Republic has been stalling for time while continuing to develop its nuclear program.

The letter could serve to ratchet down what have been growing tensions between the White House and Congress over the status of negotiations and whether lawmakers should put in place a new sanctions regime in the event talks fail to curtail Iran’s nuclear ambitions.

State Department spokeswoman Jen Psaki stopped short of praising the move by the Democratic senators, but made clear the administration wants more time for the talks.

“Broadly speaking, while the negotiations are ongoing and there’s room and an opportunity for the negotiators to make progress… we think sanctions legislation could hurt that effort,” she was quoted as having told reporters Tuesday.