California voters will decide in November whether to guarantee the right to an abortion in their state constitution, a question sure to boost turnout on both sides of the debate during a pivotal midterm election year as Democrats try to keep control of Congress after the US supreme court overturned Roe v Wade.

The court’s ruling on Friday gives states the authority to decide whether to allow abortion. California is controlled by Democrats who support abortion rights, so access to the procedure won’t be threatened anytime soon.

But the legal right to an abortion in California is based upon the “right to privacy” in the state constitution. The supreme court’s ruling declared that a right to privacy does not guarantee the right to an abortion. California Democrats fear this ruling could leave the state’s abortion laws vulnerable to challenge in state courts.

To fix that, California lawmakers on Monday agreed to put a constitutional amendment on the ballot this year that would leave no doubt about the status of abortion in California.

The amendment would declare that the state “shall not deny or interfere with an individual’s reproductive freedom in their most intimate decisions, which includes their fundamental right to choose to have an abortion and their fundamental right to choose or refuse contraceptives”.

California joins Vermont in trying to protect abortion in its state constitution. The Vermont proposal, also on the ballot this November, does not include the word “abortion” but would protect “personal reproductive autonomy” – although there is an exception “justified by a compelling state interest achieved by the least restrictive means”.

Meanwhile, four conservative states – Alabama, Louisiana, Tennessee and West Virginia – have constitutions that say a right to an abortion is not protected, according to the Guttmacher Institute, an abortion rights group.

The amendment in California is part of Democrats’ aggressive strategy to expand access to abortion in response to the US supreme court’s ruling. Last week, Gavin Newsom signed a law aimed at shielding California abortion providers and volunteers from lawsuits in other states – a law aimed at blunting a Texas law that allows private citizens to sue people who help women in that state get an abortion.

California’s massive budget includes more than $200m to expand access to abortion in the state. The money would help pay for abortions for women who can’t afford them, scholarships for abortion providers and a new website listing all of the state’s abortion services in one place.

The budget also includes $20m to help women pay for the logistics of an abortion, including travel, lodging and child care. But the Newsom administration says the money can’t be used to help women from other states where abortion is illegal or severely restricted come to California to get the procedure.

A dozen other bills are pending that would support those seeking and providing abortions such as allowing some nurse practitioners perform abortions without the supervision of a doctor and block disclosure of abortion-related medical records to out-of-state entities.