FIRST ON FOX: Republican lawmakers are urging President Biden to take "decisive action" on the fentanyl crisis -- noting a significant increase in the amount of the deadly drug seized at the southern border, and expressing "deep concern" over what they say is inaction by the administration.

More than 10,586 lbs of fentanyl were seized at the southern border in FY 2021, up significantly from the 4,558 lbs in FY 2020 and 2,633 in FY 2019. Customs and Border Protection (CBP) last month said it had seen a "substantial increase" in fentanyl seizures.

REPUBLICAN ATTORNEYS GENERAL CALL FOR ACTION ON 'FENTANYL SCOURGE' FROM CHINA, MEXICO

While this number shows an increase in successful interceptions of the drug by law enforcement, Republicans have expressed concern that, like with the amount of migrants coming to the border, it indicates that greater amounts are coming north and could be getting through elsewhere past border authorities.

The U.S. Drug Enforcement Administration is seeing a record number of seizures of fentanyl. (Courtesy DEA) (DEA)

The 18 lawmakers, led by Reps. Brett Guthrie, R-Ky., and Cathy McMorris Rodgers, R-Wash., wrote to Biden warning of rising drug overdoses in recent years, and criticized his failure to mention the fentanyl issue during his one-year press conference as well as his administrations "unwillingness to secure the border" since being in office.

"Families who have lost loved ones from a drug overdose across the country deserve decisive action on this issue," they write in a letter to the White House. "Your administration’s inaction of cause for deep concern."

FENTANYL OVERDOSES BECOME NO.1 CAUSE OF DEATH AMONG US ADULTS, AGE 18-45: ‘A NATIONAL EMERGENCY’ 

The letter also criticized efforts by the Biden administration to offer grants to safe smoking and syringe programs, and the Department of Justice collaborations with operators of safe injection sites. They also criticize a proposal by the administration related to fentanyl analogues -- fentanyl-related substances that can be even more potent than fentanyl itself.

"Your administration’s proposal would exempt these substances from quantity-based mandatory minimum sentences," they write. "We are deeply concerned that scheduling these analogues without the necessary criminal penalties will incentivize traffickers to make new variations of these positions in order to evade law enforcement."

The lawmakers ask Biden if addressing fentanyl is a "top priority" for the administration, and what its plan of action is to combat the issue. Separately they request answers to a number of questions about the policy on fentanyl analogues -- including whom it consulted, and the data used to make the decision.

A recent report by the bipartisan Commission on Combating Synthetic Opioid Trafficking said the source of fentanyl into the U.S. has evolved from 2014-2019, when most fentanyl came in from China via international mail. Now, the report said, it comes in from Mexico via the land border.

CLICK HERE TO GET THE FOX NEWS APP

 "The drug is manufactured in illegal laboratories there using precursors from Asia – mainly the [People’s Republic of China] – and is trafficked principally by land into the United States."

Last month, Florida Attorney General Ashley Moody called on President Biden and congressional leadership to take "immediate and forceful action to regain control" of the border.

"As we recognize the President’s first year in office, we cannot ignore the fact that the escalating crisis at the border is having a devastating effect on our efforts to end the national opioid epidemic and save lives," she wrote