Republican lawmakers say the Obama administration's controversial “ransom” paid to Iran earlier this year is fueling a new wave of harsh sentences being handed down in the country to Iranian-Americans. 

“President Obama’s cash ransom payment to Iran makes Americans more vulnerable and encourages unjustified prison sentences and blatant kidnapping like this,” Florida GOP Sen. Marco Rubio told FoxNews.com on Wednesday.

“Senior Justice Department officials warned the White House that Iran would view the pallets of cash as ransom, but the president didn’t listen, and now Iran is taking more hostages and demanding more money.”

Rubio made the comment after Robin Shahini, who had been living in San Diego, was reportedly sentenced Monday to 18 years for "collaboration with a hostile government."

A week earlier, Iran announced 10-year prison sentences each for Iranian-American businessman Siamak Namazi and his 80-year-old father, Baquer Namazi.

The sentencings follow a deal in January that freed Washington Post journalist Jason Rezaian and three others -- an agreement completed the same day the U.S. made a $400 million cash delivery to Iran. 

The Obama administration has said the January payment was part of a $1.7 billion settlement in connection with a decades-old arbitration claim between the countries. But Rubio and other top Republicans have sharply questioned the timing, joining GOP presidential nominee Donald Trump in describing the money drop as “ransom.” 

The new sentences are reviving concerns that Tehran increasingly views such prisoners as bargaining chips. 

The Namazis were convicted for “cooperating with the U.S government against Iran,” according to NPR.

Friends and family members told the news outlet that Baquer, an international business consultant, was arrested a few months after going to Iran in 2015 for business. However, they said they did not know the details of the charges.

“Once again Iran has made a mockery of its own legal system in convicting wrongfully detained Iranian-Americans,” California GOP Rep. Ed Royce, chairman of House Foreign Affairs Committee, said after reports of the Namazis’ sentencing.

The State Department last week said the Namazis were “unjustly detained” and called for their immediate release.

The department also said U.S. officials are especially concerned by reports of the elder Namazi's "declining health and well-being.”

Lawmakers also have suggested that Iran has been further empowered by the U.S.-led international pact signed in July 2015 in which Tehran agreed to curb its development of a nuclear weapon in exchange for countries lifting billions in sanctions.

The 46-year-old Shahini, a graduate student, was reportedly sentenced after a brief, secret trial. Shahini has acknowledged supporting the protests that followed Iran's disputed 2009 presidential elections. But he denies being involved in spying, reportedly saying in a call from prison that the evidence against him consists of pictures he posted on social media.

The State Department said in a statement: "We reaffirm our calls on Iran to respect and protect human rights and fundamental freedoms, cease arbitrary and politically motivated detentions and ensure fair and transparent judicial proceedings."

Shahini was detained in July while going to Iran to visit his mother, who had been diagnosed with Alzheimer's disease. He vowed after his sentencing to go on a hunger strike.

Iran does not recognize dual nationalities, meaning that those it detains cannot receive consular assistance. In most cases, dual nationals have faced secret charges in closed-door hearings before Iran's Revolutionary Court, which handles cases involving alleged attempts to overthrow the government.

Still missing is former FBI agent Robert Levinson, who vanished in Iran in 2007 while on an unauthorized CIA mission.

The GOP-led House several weeks ago passed a Royce-sponsored bill to stop future cash payments to Iran.

“There will be no more secret planes full of cash to fund Iran’s terrorism,” he said before the vote. "From the start, Iranian military commanders were calling it ransom.”

The Associated Press contributed to this report.