FBI agents working without pay during the government shutdown have a message for politicians: Financial security is national security. With thousands of FBI agents set to miss their first paychecks Friday as the partial government shutdown draws out into Day 20, the union representing them is urging Congress and the White House to renew funding for the law enforcement agency immediately, saying dwindling bureau funds will imperil critical operations."As the shutdown continues, Special Agents remain at work for the American people without being paid, and FBI leadership is doing all it can to fund FBI operations with increasingly limited resources — this situation is not sustainable," the union representing the majority of 13,000 FBI special agents said in a petition to the White House and Congress released on Thursday. "The important work done by the Bureau needs to be funded immediately."While the FBI has furloughed about 5,000 employees, including analysts and lawyers, it has kept the vast majority of its special agents working in the field to ensure critical law enforcement operations continue. Those agents, like nearly 400,000 other "essential" government employees, have been required to work without pay during the shutdown.That has ensured that FBI operations have continued unimpeded. But as the shutdown, which began Dec. 22, drags on with no end in sight, it's likely to take a toll on both operations and the agents that run them, said Thomas O'Connor, president of the FBI Agents Association."This is not about politics for special agents," O'Connor said during a press call with reporters. "For special agents, financial security is national security."The effect of the shutdown is likely to ripple beyond FBI investigations, O'Connor said. While agents missing debt payments could see their security clearance restricted, others might be encouraged to look for more financially stable jobs.The partial government shutdown began after the White House and Congress failed to reach an agreement over funding for a wall along the U.S.-Mexico border.Two unions representing government employees have taken the Trump administration to court over the shutdown.The National Treasury Employees Union, which represents 150,000 federal employees including Customs and Border Protection officers, on Thursday sued the administration, saying requiring government employees to work without pay during the shutdown is a violation of the Fair Labor Standards Act. The American Federation of Government Employees, the largest union of federal employees, filed a suit against the administration on Dec. 31, alleging it was illegally forcing hundreds of thousands of workers to work without pay.