FIRST ON FOX: Republican senators, led by Sen. Roger Marshall, R-Kansas, are raising concerns about a ‘significant threat’ to national security posed by an increase in Chinese nationals at the southern border — who the lawmakers say are being almost entirely released into the U.S. and could have ties to the Chinese Communist Party.

The lawmakers wrote to DHS Secretary Alejandro Mayorkas expressing concern about the approximately 18,000 Chinese nationals who have been encountered at the southern border this fiscal year. That’s compared to just over 2,000 in FY 2022, and just 450 in FY 2021.

They note that numbers have continued to increase and that the overwhelming majority are single adults. Lawmakers signed onto the letter include Sens. Mike Braun, R-Ind., Pete Ricketts, R-Neb., Marco Rubio, R-Fla., and Thom Tillis, R-N.C.

‘July set the record for nationwide encounters with Chinese nationals with just over 6,100. 94.8 percent of Chinese national encounters in FY23 have been single adults,’ they say. ‘This trend poses a significant threat to our national security and warrants immediate attention and action from the Department of Homeland Security (DHS).’

They go on to say that ‘it is our understanding that not a single one of these individuals encountered has been detained for any length of time but rather benefited from this administration’s policy of catch and release.’

They note prior concerns, including from Republicans in Congress, that some of those single adults could potentially be tied to the Chinese Communist Party.

They say that there could be among those coming across ‘individuals who could engage in espionage activities or cyber-attacks against our critical infrastructure, government agencies, or private sector entities.’

‘There have been numerous documented instances of Chinese nationals, at the direction of the CCP, engaging in espionage, stealing military and economic secrets,’ they say. They also highlight the role China plays in providing precursors to Mexican drug cartels, which are then used to create fentanyl – which is then transported across the U.S. border.

The lawmakers ask a series of questions to Mayorkas, including how it identifies those from China and any potential ties to the CCP or its Peoples Liberation Army. It also asks how many Chinese nationals have been apprehended, released and deported from the United States, and how many nationals Chinese has refused to repatriate.

Lawmakers also want to know what actions are being taken to address the issue, including discussions with China and Mexico. DHS itself has recently noted the national security threat from China. In its most recent threat assessment, DHS warns China will likely use predatory economic practices, including espionage and market manipulation, against the U.S.

In a statement to Fox News Digital, Marshall said that the increased number of single adults coming from China ‘must be a wake-up call within the Biden administration.’

‘We cannot allow the CCP to undermine law and order here on U.S. soil, whether it’s funneling fentanyl into our communities, stealing our intellectual property, setting up CCP spy police stations across the country, infiltrating our public school curriculum, or flying a massive spy balloon through our heartland the Biden Administration has been an abysmal failure when it comes to holding China accountable,’ he said.

The letter comes amid a broader spike in migration at the border. After a relative lull in June, numbers have shot up in July and August and look set to continue in September. Border Patrol facilities have been overwhelmed and have resorted to releases onto the streets in multiple sectors.

Sources have told Fox that there have been multiple days this week of over 8,000 illegal immigrant encounters ad that there are expected to be around 230,000 migrant encounters in August. That 230,000 would be up significantly from over 180,000 in July and 144,000 in June. August’s numbers would mark the highest month in 2023.

Republicans have hammered the administration on the crisis and sought to pass a sweeping border security bill to restart wall construction and limit the use of asylum and parole authorities.

The administration has called on Congress to provide additional funding and to pass an immigration reform bill Democrats introduced in 2021 to fix what it says is a ‘broken’ system.