To some election law experts, dire warnings by vocal activists that faulty voting machines are threatening democracy tend to ring false.

After all, questionable machines are only one of the many problems plaguing an election system that's outmoded, decentralized and chronically underfunded. The best machines in the world won't help if local election officials can't hire and train enough poll workers and clean up their error-riddled voter registration lists.

But an industry shakeup that's placed one controversial vendor in charge of more than half the nation's voting technology has thrust the debate over machines squarely back into focus.

The sale earlier this month of Diebold Inc.'s election business to Election Systems and Software has alarmed election officials and civic watchdogs, and prompted calls on Capitol Hill for the Justice Department to intervene. A smaller, competing voting machines manufacturer has also filed suit.

"This acquisition may have serious adverse implications for how our country votes," wrote Sen. Charles Schumer, D-N.Y., in a letter to Attorney General Eric Holder. Schumer, who chairs the Senate Rules and Administration Committee, urged the Justice Department to review the deal, which would give ES&S control of the election systems in 68 percent of the nation's voting precincts.

State and local election officials are watching closely to see where legal challenges and a possible federal investigation may lead.

"I am deeply concerned that local governments and taxpayers will not be getting a fair deal because too much market power will be held in too few hands," Schumer wrote. Watchdog groups BlackBoxVoting.org and Common Cause also are urging the Justice Department to thoroughly review the deal.

Texas-based vendor Hart Intercivic Inc., a smaller competitor to ES&S, also has filed suit in U.S. District Court in Delaware to enjoin the sale, which principally involved Diebold subsidiary Premier Election Solutions. The acquisition violates the 1914 Clayton Act and the 1890 Sherman Act, the suit alleges, and amounts to a "conspiracy to monopolize the market for voting machines."

"This is one of the only markets you'll find that is of potential interest to every citizen in the United States," said Patton Boggs attorney Jonathan Rubin, who is representing Hart Intercivic, on a radio program produced by Patton Boggs. Hart is seeking both an injunction to stop the sale and damages for allegedly anticompetitive business practices.

In an interview, Rubin said the absence of market competition threatens to weaken the quality of voting machines, which has already been called into question. Hart's customers "experience high satisfaction rates and are overwhelmingly loyal," the suit alleges, while both Diebold and ES&S "are overwhelmingly criticized by election officials responsible for procuring systems." The suit details complaints from election officials in Pennsylvania, Ohio and Indiana over "deception," price gouging and "unsavory business practices."

ES&S officials countered in a statement that the company "is disappointed by the recent legal action initiated by one of our competitors," and will "vigorously defend" itself against the lawsuit and against "grossly false and misleading claims made in the complaint."

Both Diebold and ES&S have been dogged by lawsuits and controversies in California, Ohio and elsewhere over contracting disputes and machines that allegedly lost or "flipped" votes. Activists advocating a voter-verified paper trail have long complained of subpar technology and secretive practices by voting machine vendors who fail to publish the source codes for their software.

"We've got equipment out there that's unverifiable, and lacks transparency and oversight," said Warren Stewart, legislative policy director for VerifiedVoting.org. "That existed before this merger, and after this merger, and that needs to be addressed whatever happens with this sale."

Still, state and local election officials are watching closely to see where legal challenges and a possible federal investigation may lead. Some have voiced concerns that consolidation in the industry could make it harder for election administrators to negotiate affordable contracts and will lessen both competition and innovation.

California Secretary of State Debra Bowen "has many unanswered questions on behalf of voters, county election officials and taxpayers," said her spokeswoman, Nicole Winger. In March, California settled a lawsuit with ES&S for $3.25 million following a dispute over machines that contained hardware changes not approved by the state. A leading question is whether ES&S will honor state contracts involving already-purchased Premier voting machines, Winger said, or whether California officials will now be forced to go out and purchase a new round of costly voting machines.

It's not the first time that ES&S has found itself in the midst of an antitrust dispute. When ES&S formed in 1997, following the acquisition of Business Records Corp. by American Information Systems, the Justice Department intervened. The department forced the divestiture of the optical scan and voting equipment business to another company, Sequoia Voting Systems. Since then, as Schumer's letter to Holder notes, the number of voting systems manufacturers has only decreased.

"We need to deploy a system that our election administrators and voters can understand and trust, and we're not there yet," said Candice Hoke, an election law professor at Cleveland State University who endorses robust post-election audits to assess voting machine performance. Rep. Rush Holt, D-N.J., in March reintroduced the Voter Confidence and Increased Accessibility Act, which would create national voting standards, require paper ballot voting systems and require routine, random audits.

They're all steps that would, over the long term, improve the transparency and accountability of voting systems. In the meantime, the threat of an industry monopoly merits immediate federal scrutiny.