Two fugitive bankers from Ecuador, whose relatives made political donations to Sen. Robert Menendez (D-New Jersey) and other leading politicians in the hopes of avoiding extradition, have been arrested by immigration agents in Florida.

Homeland Security officials said William and Roberto Isaias have been in the U.S. illegally for years, living in Florida and running their businesses there after fleeing Ecuador, where they were convicted in absentia in 2012 of embezzlement.

The Isaias brothers have long been suspected of moving some of their ill-gotten millions into the U.S. The pair vehemently deny any wrongdoing.

Relatives and employees of the brothers have donated more than $300,000 to U.S. political campaigns since 2010 amid the brothers' ongoing efforts to avoid being sent back to Ecuador to serve their prison sentences. Their arrests this week come after NBC New York in 2014 first revealed the brothers' presence in Miami and the family’s political donations.

"U.S. Immigration and Customs Enforcement’s (ICE) Homeland Security Investigations (HSI) arrested unlawfully present Ecuadorian nationals William and Roberto Isaias in Miami Feb. 13," said ICE Miami spokesman Nestor Yglesias. "Both men were then transferred to ICE’s Enforcement and Removal Operations and are presently in agency custody pending removal proceedings."

The spokesman would not say why the arrest took place now after years of their living in large homes and running businesses in the Miami area.

More than $100,000 in Isaias family donations went to members of Congress over the years, including Menendez and Republican Sen. Marco Rubio. Menendez was among several congressional members who wrote letters to the State Department and the Department Homeland Security in support of the Isaias brothers amid their immigration struggles.

Menendez couldn't be reached for comment Friday, but in an interview on MSNBC on Saturday, the senator defended the bankers.

"This is a family that was persecuted by the then-president of that country, who took their television [stations] and took their free media, ultimately by state control, and ultimately took them," he said. "Everything our government has independently investigated found they were wrongly pursued. If they had been correctly pursued, then there would have been a grant of extradition by the Bush administration, a Republican administration or the Obama administration, a Democratic administration."

"So therefore, I think that it's pretty clear... on a bipartisan basis.. . that these are trumped-up charges," he maintained.

But several past U.S. ambassadors to Ecuador had called for the brothers to be deported. In 2005, then-U.S. Ambassador Kristie Kenney in a diplomatic cable said the brothers "...used their ill-gotten wealth to buy safe passage from Ecuador and later pressured prosecutors to reduce criminal charges against them."

Former U.S. Ambassador Linda Jewell also repeatedly voiced concern about the Isaias brothers' presence inside the United States. But Justice Department officials had said past extradition filings by Ecuador’s government lacked sufficient proof.

In December, Florida’s State Supreme Court let stand a civil suit by the government of Ecuador against the Isaias brothers. Plaintiff attorney Alvin Davis said they are seeking about $1 billion dollars in damages from the Isaías brothers for their banking crimes.

"It’s about time," Davis said. "Someone has lifted the protective curtain around them."

Davis pushed back against Menendez’s claims on MSNBC. He said it is not correct that past extradition requests were turned down because they were without merit. The U.S. Justice Department wanted additional information and the process is ongoing.

In 2012, Isaias relatives also gave $100,000 to the Democratic Party around the time another relative, Estefania Isaias, was accused of visa fraud by the State Department. She denies the allegations that she improperly smuggled maids into the U.S. from Ecuador to work at the Isaias’ Miami homes. Menendez wrote letters and made phone calls to try to help Estefania Isaias obtain permission to stay in the U.S. after the fraud allegations had surfaced. She was never charged and was permitted to stay in the country.

The Isaias family has said the charges against the bankers were politically motivated by a corrupt Ecuadorean government. Reached by phone, Xavier Castro, a close friend and one-time lawyer for the brothers in Ecuador, said the arrest is "unfortunate" and "disappointing" but that he did not know which attorney was handling the brothers’ immigration case in Miami.

A government source familiar with the Miami detention said William and Roberto Isaias are expected to remain in immigration custody pending removal hearings.

The Isaias brothers' presence in Florida has been a source of contention between the U.S. and Ecuador for years. The two governments have also been debating the presence of fugitive Wikileaks founder Julian Assange at the Ecuadorian Embassy in London.