Federal employee safety and Homeland Security Department workforce issues dominated the agenda Tuesday during the opening of a three-day National Treasury Employees Union legislative conference in Washington.

NTEU President Colleen Kelley said recent attacks on government facilities and anti-government rhetoric have "created an environment where federal employees are concerned about their safety."

In the aftermath of the February airplane attack that burned a federal office building in Austin, Texas, to the ground and killed an Internal Revenue Service employee, the Treasury Inspector General for Tax Administration has received reports of more than 70 threatening phone calls, according to Kelley. Targets of audits and investigations have made comments about "taking flying lessons" and other menacing statements to IRS employees nationwide, she said.

"I cannot imagine any scenario after the Austin attack where that's appropriate," she said. The IG is taking all reports seriously and investigating them, she added.

Meanwhile, Austin IRS employees returned to work at two separate temporary locations on Monday. The agency is looking into a permanent location for a new office, and has hired a contractor to help employees recover personal items and files from the ruins of the old building. Officials also set up hotlines for citizens who are concerned about the attack's effect on their tax proceedings.

Kelly noted that President Obama expressed concern about the Austin incident and last week's shootout at an entrance to the Pentagon. She shared a March 9 letter from the president with conference participants.

"The events of recent weeks have again reminded us of the risks that federal civilian employees face in service to our nation," Obama wrote. "Our Constitution's vision of 'a more perfect union' is only possible because of their tireless efforts. My administration is fully committed to maximizing the safety of federal employees and preventing acts of violence against them."

Sen. Barbara Mikulski told conference participants the incidents are on her mind as well. "I worry about you being on the front line," the Maryland Democrat said. "I worry about you being on the firing line because of the kind of work you do."

The House Oversight and Government Reform subcommittee that handles workforce issues has scheduled a hearing next week on federal office security. On the Senate side, Sen. Joseph Lieberman, I-Conn., chairman of the Homeland Security and Governmental Affairs Committee, plans to introduce a bill aimed at enhancing federal building security.

NTEU's conference also focused on security employees.

Rep. Nita Lowey, D-N.Y., told the union's members there was a direct connection between work conditions at the Transportation Security Administration and aviation safety. Lowey has introduced legislation that would grant TSA screeners collective bargaining rights -- an issue that has long been a priority for NTEU.

"Transportation Security officers are the first line of defense in detecting and preventing terrorism in air travel," she said. "The jobs are critical. You know that. And this should be a workplace that reflects how critical the jobs are."

The union also said it will advocate a new career path for certain experienced workers at DHS' Customs and Border Protection bureau. NTEU would like CBP to set these workers' pay at the GS-12 level rather than GS-11, to reflect new and expanded job responsibilities. CBP announced it would do that, but has backed away from the plan, citing budgetary concerns.

In addition, Maureen Gilman, the union's legislative director, said NTEU would push lawmakers to restore funding for a program that granted CBP employees awards of up to 5 percent of their pay if they demonstrated foreign language proficiency and used those skills on the job.

Gilman noted the union already was working with military groups to try to win a higher pay raise for service members and civilian employees, and to ensure pay parity. President Obama in February called for a 1.4 percent pay raise for civilians and military members in 2011.