WASHINGTON — In the wake of the terrorist attacks in Brussels, a group of lawmakers in Congress is pushing to increase funding to provide better security on U.S. mass transit systems.

On Wednesday, 66 House Democrats urged the Homeland Security appropriations subcommittee to set aside $105 million to help local transit systems improve security. That’s $20 million more than President Obama requested in his 2017 budget proposal and a drop in the bucket compared to the billions the country spends annually on aviation security.

Members of Congress from California and Washington state to North Carolina to Florida are expressing worry that U.S. transit systems, including the busy subways in New York City and Washington, D.C., are vulnerable to a similar attack.

“This week’s horrific terrorist attacks in Brussels – one of which targeted a busy subway station – underscore the pressing need to keep America’s bus, rail and ferry systems safe,” said Rep. Eric Swalwell, a California Democrat who is a member of the House Permanent Select Committee on Intelligence.

Swalwell and other lawmakers also requested that the Transit Security Grant Program, administered by the Federal Emergency Management Agency, be kept separate from other security preparedness grants.

The funding for transit security is paltry compared to the $7.6 billion requested in next year’s budget for the Transportation Security Administration, the agency that focuses primarily on aviation security. Unlike air passengers, rail transit, ferry and bus passengers are generally not screened before they board.

According to the American Public Transportation Association, Americans took 10.8 billion transit trips in 2014, the highest level of ridership in 58 years.

The nation’s transit systems were supposed to get more security funding from FEMA under the 9/11 Commission Act of 2007. But since 2011, the Transit Security Grant Program has provided less than $100 million a year.

“An attack on any of these systems could kill thousands, flood rail tunnels and stations, and cripple major metropolitan areas,” the lawmakers wrote.