In a speech on the Senate floor, Mitch McConnell on Wednesday denounced Democratic legislation intended to increase voter turnout as a “power grab,” singling out one proposal as particularly nefarious: making Election Day a federal holiday.

“This is the Democrat plan to restore democracy?” said Mr. McConnell, Republican of Kentucky and the Senate majority leader, chuckling to himself. “A power grab that’s smelling more and more like exactly what it is.”

His remarks set off a backlash from Democrats in Congress, who questioned why anyone would oppose efforts to clear obstacles for voting. The criticism extended to social media, where people accused Mr. McConnell of being afraid of increased voter turnout. Republicans have often put forward measures, like laws requiring voter identification or restricting early voting, that Democrats say are devised to suppress turnout.

“Is it a Democratic Party ‘power grab,’ as Mitch says, if we make voting more convenient for everyone?” former Senator Barbara Boxer, Democrat of California, said on Twitter on Thursday. “What is Mitch afraid of? Answer: the people.”

Representative Ted Deutch, a Florida Democrat, shared a video of Mr. McConnell’s remarks and said, “An Election Day holiday WOULD be a power grab,” adding: “It would be the American people grabbing power back from the wealthy special interests that dominate Washington because @senatemajldr & others prefer that it be hard to vote.”

The target of Mr. McConnell’s comments, a House of Representatives bill titled For the People Act of 2019, is the first major legislation by the new Democratic-controlled House and puts forward seven major changes to elections nationwide. The proposals are wide ranging, including changes to how people register to vote and new requirements for states to secure voting systems.

Among the proposals: Voters could register in person on the day of an election, an option that is currently offered in only 18 states and the District of Columbia, and could cast ballots in federal elections during an early-voting period, which all but 11 states already allow. Permitting same-day registration could increase voter turnout by three percentage points, the equivalent of about 3.8 million additional voters in the 2016 presidential election, according to studies. The bill would also allow automatic registration for eligible people.

The bill also seeks to remove a major hurdle that prevents people from voting: work. A census survey of roughly 19 million registered voters who did not participate in the 2016 election found that 14.3 percent, or about 2.7 million people, said they were too busy to vote. The legislation proposes making Election Day, the first Tuesday in November, a public holiday just like Washington’s Birthday, Independence Day and Christmas.

It would grant the federal government’s two million full-time employees a paid day off, and would make companies, many of which shut down on federal holidays, more likely to grant their workers a day off. Mr. McConnell derided that idea as “generous new benefits for federal bureaucrats and government employees.”

“Just what America needs: another paid holiday,” said Mr. McConnell, echoing comments he made about the bill in an op-ed essay in The Washington Post this month.

The broad legislation from Democrats also targets hot-button issues surrounding voter suppression and the fairness of elections. To combat gerrymandering, the bill would strip the power to set congressional boundaries from state legislatures, 30 of which are controlled by Republicans, and hand it over to new independent commissions. And to try to counteract the influence of money in politics, the bill would move toward public financing of elections.

The bill would also weaken voter identification laws in states by allowing voters without identification to vote if they provide a “sworn written statement.” Republican advocates of such ID restrictions insist that they are needed to stop voter fraud, though studies have concluded that in-person fraud is very rare. Democrats have criticized the measures as attempts to suppress the votes of people of color.

Voter turnout in the United States is fairly low compared with most other developed countries. About 56 percent of voting-age Americans cast ballots in the last presidential election, a slight increase from 2012 but lower than 2008, according to the Pew Research Center. In Germany, by comparison, voter turnout in 2017 was 76 percent.

Some countries with the highest turnout in the world make it easier for their citizens to cast ballots. In Australia, voting is required by law, and citizens also make a party out of it: Elections are held on Saturdays, with people gathering for barbecues and get-togethers. Turnout is typically over 90 percent.

Also high on the list, according to Pew: Israel and South Korea, which both have national holidays on their election days.