At least 18 US states have enacted more than two dozen laws this year that restrict voting access, according to a new report from the Brennan Center for Justice.

The report found that the 30 laws that have been passed since 1 January “make mail voting and early voting more difficult, impose harsher voter ID requirements, and make faulty voter [roll] purges more likely, among other things”.

The laws were among the more than 400 bills introduced in 49 states during this year’s legislative session that would make voting more difficult.

Such proliferating and restrictive legislation contrasted sharply, however, with the report’s finding that no states produced evidence of widespread fraud in the 2020 elections, despite continued claims by Donald Trump, backed by numerous Republican leaders, that he was not beaten by Joe Biden in the race to the White House.

In fact, officials at local, state and national level declared last November’s the most secure election in US history, while Trump fought in vain through the courts to overturn the result.

The Brennan Center notes that not all of the 30 laws are equally restrictive. Four laws in Indiana, Kentucky, Louisiana and Oklahoma, for instance, also included legislation that will make voting easier for certain communities.

Still, the study says the “wave of restrictions on voting” is “the most aggressive we’ve seen in more than a decade of tracking state voting laws”.

The New York-based public policy organization blames voter fraud allegations and racist misinformation for the rise in voter suppression efforts.

The news followed the release of a letter sent to Biden earlier this week from the Leadership Conference on Civil and Human Rights asking for the administration to renew its commitment to passing the For the People Act and the John Lewis Voting Rights Advancement Act, legislation that has so far been stymied in Congress by the Republicans.

The letter was signed by a number of organizations, including the Brennan Center for Justice, Black Voters Matter Fund, Color Of Change and the NAACP.

“As organizations dedicated to the protection of voting rights, we are just as troubled as you by the surge this year of state legislation restricting access to the franchise,” the letter said.

It continued: “Voters of color will bear the brunt of these new restrictions, in what amounts to the most significant assault on voting rights since the Jim Crow era. Even more serious threats loom on the horizon. The upcoming redistricting cycle is expected to bring another round of extreme gerrymandering that will disproportionately dilute the votes of people of color.”

It urged action, noting: “Congress has the power and duty to stop this anti-democratic and discriminatory assault on Americans’ voting rights. Indeed, only federal legislation can ensure that our elections are safe and free and fully protect the franchise.”