The Obama administration is stepping up pressure on the Senate to hold off on another round of Iran sanctions as Western powers test Tehran’s willingness to scale back its nuclear aims.

Vice President Joe Biden, Secretary of State John Kerry and Treasury Secretary Jack Lew planned to meet with the Senate Democratic leadership and members of the Senate Banking Committee late Thursday in hopes of convincing lawmakers to delay plans to meet next week and draft a new package of penalties.

Although the White House insists that tough sanctions have forced Iran to negotiate, it want Congress to pause in imposing new, punitive measures to give negotiators flexibility in talks with Iran. Lawmakers argue that this is no time to let up on Tehran.

“It’s working,” said Sen. Richard Shelby, R-Ala., a member of the Banking Committee. “It’s pinching the economy of Iran and that’s what we ought to keep doing as much as we can and as fast as we can.”

Unnerving for the administration is the prospect that a Senate panel would be crafting new sanctions at the same time as Iran and six world powers meet in Geneva next week for another round of negotiations.

Western powers have been trying to determine Iran’s seriousness in complying with demands it prove its nuclear program is peaceful since reformist President Hassan Rouhani took office in August. Both sides described their last round of talks as positive, with Tehran ready to discuss some curbs on programs that can create both atomic energy and the fissile core of nuclear arms.

The Banking Committee is weighing a bill that would blacklist Iran’s mining and construction sectors. It largely mirrors a House measure that passed overwhelmingly by a 400-20 vote in July. That bill also called for all Iranian oil sales to end by 2015.

The Senate bill may narrow that time frame, block international investment in more economic sectors, try to close off Iran’s foreign accounts and tighten President Barack Obama’s ability to waive requirements for allies and key trading partners who continue to do business with Iran.

Administration officials met last week with Senate staffers and made their case to some American Jewish groups during a White House meeting earlier this week.

The powerful American Israel Public Affairs Committee, which has considerable sway in Congress, favors more sanctions to stop Iran.

Administration officials say Obama is not seeking an open-ended delay to new sanctions and believes there may come a point where additional economic penalties against Iran are necessary. Officials say the administration is also emphasizing to lawmakers and outside groups that the president wants to keep the current sanctions regime in place while negotiating with Iran.

Even if the administration succeeds in convincing Democratic leaders and Senate Banking Chairman Tim Johnson, D-S.D., to delay a vote, proponents of tough sanctions such as Sen. Mark Kirk, R-Ill., are likely to try to attach new sanctions to the annual defense policy bill that the Senate could consider as early as the week of Nov. 12.

(AP)