“The legislation we added to the FAA bill before the Senate is critical to addressing holes in our nation'sairport security. I hope my colleagues will pass the FAA bill this week, and I will continue to work to address the weaknesses in our nation's transportation security and counter current and future threats.”

As the U.S. Senate prepares to vote today on the Federal Aviation Administration Reauthorization Act of 2016, CNN.com published an op-ed by Sen. John Thune (R-S.D.), chairman of the Senate Committee on Commerce, Science, and Transportation, on bipartisan airport security enhancement proposals included in the legislation following recent attacks by ISIS.

(CNN) - Last month, 35 innocent people, including four Americans, lost their lives when ISIS attacked a subway station and airport terminal in Brussels. This was just the latest in a string of attacks ISIS has orchestrated or inspired against Western targets over the past two years -- attacks that have killed more than 650 people.

If the Brussels attacks reminded us of anything, it was that ISIS must be confronted.

More specifically, the attacks reminded us that we need to confront the threat ISIS poses to our nation's transportation system. Terrorists have made a habit of targeting airports, subways and other transit hubs, as they did in Belgium, because of the opportunity these locations offer for mass casualties.

I'm proud that legislation I developed to address holes in our nation's airport security was recently added to the Federal Aviation Administration bill being considered by the Senate.

When people think about airport security, the first thing that usually comes to mind is passenger screening. But airport security involves a lot more than that.

One key element of airport security that doesn't get as much news coverage is the need to make sure that individuals who work behind the scenes at airports don't pose a security risk. For example, many experts believe that ISIS' attack on a Russian flight from Egypt in October, an attack that killed 224 people, was facilitated in part by an airport worker.

Before they can take up their jobs feeding travelers, maintaining airplanes, transporting baggage and running other necessary operations, airport workers must obtain what is known as a Secure Identification Display Area badge, which is issued by an individual airport according to requirements established by the Transportation Security Administration. Too often, however, these badges have been issued to individuals who have no business holding them.

Over the past few weeks alone, a number of vetted aviation sector employees have been caught in alleged criminal activity.

On March 18, a flight attendant was accused of abandoning a suitcase with 68 pounds of cocaine after she was confronted by airport security officials in California.

In Florida, an airline gate agent was arrested on March 26 with a backpack containing $282,400 in cash that he allegedly intended to hand off to an associate. According to news reports, the agent told authorities he was aware that the money was connected to illegal activity but knew few other details. In other words, the money could have belonged to terrorists, and this individual would have been none the wiser.

Criminals with behind-the-scenes access at airports can pose a real security threat.

For the right price, too many criminals would be happy to expand their illegal activity -- even if it involved assisting terrorists. And while very few criminals are terrorists themselves, it's not at all uncommon for terrorists to get their start as criminals. The Brussels attackers were known to the police as criminals long before they carried out terrorist attacks.

Ensuring that dangerous individuals can be barred from working in secure areas of an airport should be a no-brainer. Yet right now in the United States, applicants convicted of embezzlement, racketeering, robbery, sabotage, immigration law violations and assault with a deadly weapon can all obtain a security badge granting access to restricted areas.

The airport security amendment I offered in the Senate -- an amendment approved by an overwhelming bipartisan majority -- includes legislation developed with my Democrat co-sponsor, Sen. Bill Nelson, to address the weaknesses in airport security that have led to dangerous individuals being given security badges.

Our legislation, the Airport Security Enhancement and Oversight Act, would tighten vetting procedures for workers who are trying to get a SIDA badge and expand the list of criminal convictions that could disqualify an applicant from obtaining one.

Our bill also increases accountability and fines for airports that violate security rules, and it expands random inspections of airport workers. While some employees with SIDA badges are subject to regular or intermittent security checkpoint screenings similar to the screenings passengers face, most are not.

A badge issued to an airline ramp agent at the Atlanta airport, for example, allegedly allowed him to bypass security screening, facilitating his side business of smuggling guns onto commercial aircraft, a scheme that officials believe went on for months before he was caught.

Keeping our nation safe from another terrorist attack like those that have rocked Paris, Brussels and San Bernardino means staying alert and continuously addressing vulnerabilities.

The legislation we added to the FAA bill before the Senate is critical to addressing holes in our nation's airport security. I hope my colleagues will pass the FAA bill this week, and I will continue to work to address the weaknesses in our nation's transportation security and counter current and future threats.