WASHINGTON (JTA) — More than 70 Democrats in the U.S. House of Representatives signed a letter to President Obama supporting his opposition to new Iran sanctions.

The letter, initiated by Reps. Lloyd Doggett (D-Texas) and David Price (D-N.C.), expresses support for talks now underway between Iran and major powers on the Iranian nuclear program.

“We understand that there is no assurance of success and that, if talks break down or Iran reneges on pledges it made in the interim agreement, Congress may be compelled to act as it has in the past by enacting additional sanctions legislation,” says the letter, which has not yet been sent and which JTA obtained Tuesday from Doggett’s office.

“At present, however, we believe that Congress must give diplomacy a chance,” says the letter, first reported by The Washington Post on Monday. “A bill or resolution that risks fracturing our international coalition or, worse yet, undermining our credibility in future negotiations and jeopardizing hard-won progress toward a verifiable final agreement, must be avoided.”

Signatories were not made available, although Doggett’s office said they numbered more than 70.

Sources said they include Jewish lawmakers with strong pro-Israel records.

Obama has said he would veto legislation under consideration in the Senate that would impose new sanctions on Iran, arguing that the agreement that led to renewed talks bans new sanctions and that such a bill could collapse the international coalition that helped bring Iran to the talks table.

Proponents of the new sanctions, among them the American Israel Public Affairs Committee, say they would strengthen the U.S. hand at the talks.

The U.S. House of Representatives overwhelmingly passed a companion bill last summer, before talks started, but it is not clear today whether it would have the same support among Democrats.

“As a member of Congress who has consistently voted to impose tough economic sanctions on Iran, I believe those sanctions have worked,” Doggett said in a statement.

“In honoring our commitment to Israel, we must use all of America’s strengths, including the strength of our diplomacy, to prevent Iran from becoming nuclear-armed,” he said. “Congress should not undermine diplomacy by giving the Iranian hardliners an excuse to scuttle the negotiations.”

The new sanctions bill garnered some Democratic support in the Senate when it was introduced in December, but this has slipped away since Congress returned from its holiday break.

At a hearing convened Tuesday by the bill’s main Democratic sponsor, Sen. Robert Menendez (D-N.J.), the chairman of the Senate Foreign Relations Committee, most Democrats and at least one Republican — Sen. Jeff Flake (R-Ariz.) — said they were opposed to advancing sanctions now.

“We have to return to the tradition of aggressive diplomacy,” said Sen. Tim Kaine (D-Va.), citing as a precedent President Theodore Roosevelt’s brokering of a Russia-Japan peace.

Menendez in his opening remarks expressed concerns that the limited sanctions relief that brought Iran to the table could snowball. “We have placed our incredibly effective international sanctions regime on the line without clearly defining the parameters of what we expect in a final agreement,” he said.

Separately, Sen. Chris Murphy (D-Conn.) on Tuesday launched a citizens’ petition against new sanctions.

“Let’s give the Obama Administration and their partners the room to work out a peaceful resolution to this long-festering crisis before voting on any additional sanctions or other efforts that would undermine diplomacy,” he said in an email distributed by the MoveOn.org, a liberal activist group. The petition had garnered close to 50,000 signatures by early Tuesday evening.