FOSTER CITY (KPIX 5) — The battle for tighter restrictions on gun sales in California includes a couple of new pushes to make it more difficult to purchase firearms.

Just like there are age restrictions for buying alcohol or renting a car, it could soon be illegal to buy long guns including assault rifles and shotguns for anyone under 21 years of age in California.

An amendment to a bill was introduced in Sacramento that would raise the age requirement for people purchasing long guns from 18 to 21, just as there currently is for handguns.

“Data shows us that people age 18 to 21 disproportionally commit more gun homicides,” said Assemblyman Rob Bonta (D-Oakland)

Gun owners and members of California’s Libertarian Party strongly oppose the bill.

“You can sign up for the military at 18 and get a gun, but as a private citizen you can’t get a gun? It just doesn’t make sense to us,” said Robert Imhoff of the Santa Clara County Libertarian Party.

In the meantime, a protest held in Foster City Thursday was aimed at making it harder to buy assault weapons at any age.

About two dozen people rallied outside of Visa headquarters, calling on the credit card company to stop doing business with stores selling assault weapons.

“It’s a simple act. Visa, don’t let people use a Visa credit card to buy weapons of mass murder,” said one of the women protesting.

Amid tight security, a box full of 150,000 signatures from people around the country supporting the effort was hand delivered to a Visa representative inside the building.

Visa later denied the protester’s request, saying in a statement, “We do not believe Visa should be in the position of setting restrictions on the sale of lawful goods and services.”

Organizers said they plan to keep the heat on Visa.

“I think they will have to face the consumers who are disappointed by their inaction,” said William Winters with the Courage Campaign.

The protesters said the issue may ultimately be decided by the marketplace.