A California senator is circulating a letter in Congress that asks President Barack Obama to impose a ban on semi-automatic rifles and so-called “assault pistols” that are imported from overseas, a move some see as a backdoor attempt to restrict many popular modern sporting rifles from U.S. gun owners.

Democratic Sen. Dianne Feinstein is trying to drum up support from fellow lawmakers to urge the ATF to more broadly enforce rules set in 1998 by the Treasury Department that allows imports of rifles that are “generally recognized as particularly suitable for or readily adaptable to sporting purposes.” Feinstein argues that enforcement has been too lax, and that non-military AK variants, for example, should be banned.

“In recent years … importers of firearms have taken advantage of ATF’s interpretation of the ‘sporting purposes’ test to evade the import ban,” the letter says. “These military-style firearms are not prohibited under the current import ban, even though they are functionally equivalent to prohibited rifles with a military origin.”

She said that imported semi-automatic rifles were finding their way into the hands of Mexican drug gangs “fueling deadly violence.”

Feinstein called on the president to “take immediate action to address the significant number of assault weapons that are being imported into the United States in contravention of federal law” and therefore make good on his State of the Union pledge to make 2014 “a year of action” on gun control.

Feinstein sponsored an updated version of the 1994 “Assault Weapons Ban” in 2013 after the Newtown, Conn., school shootings which was voted down in the Senate.

After the letter was released in mid-March, the National Shooting Sports Foundation urged senators to reject the effort, calling Feinstein’s effort a “jihad against semi-automatic modern sporting rifles.”

“The U.S. Senate's leading foe of Americans exercising their Second Amendment rights is … using a different tactic,” NSSF said. “She is pursuing ‘banning’ firearms because of their characteristics and not focusing her effort on the criminals who misuse firearms.”

The letter urges the ATF to ban imports on semi-automatic rifles and “assault pistols” that can accept a magazine that holds more than 10 rounds, have a “thumbhole stock,” and it also asks the ATF to ban the import of parts that could be assembled into an “assault rifle.”