Dianne Feinstein of California, a member of the Senate's intelligence and appropriations committees, said she was "disappointed" that the White House intends to block Tehran's request for funds.
"Providing these funds to Iran would help it respond more effectively to the disease and mitigate the risk of further destabilization in the region," Feinstein said in a letter to Trump, Middle East Eye wrote on Saturday.
Amid the continuation of unilateral US sanctions, the Islamic Republic turned to the IMF for the first time in decades for funds.
Earlier this week, the Trump administration signaled that it will not allow the IMF loan to go through.
Feinstein's letter follows numerous pleas by rights groups, world leaders and US lawmakers for Washington to ease sanctions against Iran.
But Trump and his top aides claim sanctions are not affecting Iran's response to the pandemic because they do not apply to food, medicine and humanitarian assistance.
Advocates of lifting the sanctions argue that Iranians need funds to buy medical supplies and abide by economically painful social distancing measures to curb the spread of the disease.
Iran had applied for an emergency loan from the IMF known as Rapid Financing Instrument (RFI), which covers countries' urgent needs and does not require a fully-fledged reform program.
Established in 1945, the IMF provides low interest loans to countries in financial crises. The lending is often accompanied by reform policies that the recipients must agree to in order to balance their finances.
RFI loan requests are approved by the IMF executive board – a 24-member body that represents 189 countries. Voting quotas on the board are based on the countries' economic size and contributions to the organization.
IMF can still OK Iran’s loan
The United States has by far the biggest voting quota, amounting to 16.52 percent of the votes. As the biggest shareholder, Washington has huge sway over IMF policies. But even with Trump's objections, other countries can still approve Iran's plea for funds.
IMF managing director Kristalina Georgieva said on Thursday that the organization has increased funds for urgent requests and is working around the clock to meet demand for financial aid during the COVID-19 crisis.
Earlier in the week, Iranian President Hassan Rouhani warned the IMF that global public opinion will be unforgiving against the organization if it does not meet Tehran's request.
"We are paying the IMF and the World Bank our share, and part of our reserves are at their disposal," he said.
"It is not and will not be acceptable to us if they discriminate against us when considering our application for the loan. It will not be acceptable to the world public opinion either."
The Trump's administration's intention to block the loan request comes after several rounds of new sanctions against the Islamic Republic since the COVID-19 outbreak started earlier this year.
In 2018, Trump nixed the multilateral deal that saw Iran scale back its nuclear program in exchange for lifting sanctions against its economy.
Since leaving the deal, known formally as the Joint Comprehensive Plan of Action (JCPOA), the US administration has been piling on damaging sanctions against various Iranian individuals, companies and economic sectors.
But with the coronavirus spreading in and from Iran, critics of Trump's "maximum pressure" campaign have called for suspending the sanctions – not only for the sake of Iranians but the entire region, including US troops and allies – who may suffer if the virus is not contained.
"It is in our national interest and in the interest of international security, to help Iran contain this disease," Senator Feinstein wrote in her letter to Trump on Thursday, urging the US to make its support “contingent upon IMF oversight on how Iran spends the funds."