The mayor, joined by Police Commissioner Ray Kelly and a host of New Jersey mayors, spoke out against the bill at Penn Station on Sunday, four days after the gun-friendly proposal breezed through the Senate with a 68-30 vote.
"If anyone in Congress thinks that the threat of a terrorist attack on a train has gone away, they are sadly mistaken," he said according to the New York Post.
The bill, introduced by Republican Sen. Roger Wicker of Mississippi, would lift post-9/11 restrictions and allow passengers to check their locked and unloaded handguns. If Amtrak did not comply with the bill, it would lose $1.6 billion in funding.
Prior to the 2001 terror attacks, passengers could freely check their guns, but concerns over subsequent attacks led to tightened restrictions. After the 2004 Madrid train bombings, a full-blown gun ban went into effect. Wicker wants the ban tossed.
"Americans should not have their Second Amendment rights restricted for any reason," Wicker said in a statement. "Particularly if they choose to travel on America's federally subsidized rail line."
Bloomberg says he's not trying to infringe on anyone's rights.
"This has nothing to do with the Second Amendment right to bear arms and everything to do with keeping our country safe from terrorists," he said, according to the Post.
Supporters of the bill argue that new guidelines would mirror those used by the airline industry, which allow passengers to check unloaded handguns.
Bill opponents note that train stations, unlike airports, are not equipped with sophisticated screening system.