Employer groups turned out in force Monday to challenge rules proposed by the National Labor Relations Board that would streamline the process for holding union elections and make it easier for workers to organize.

The rules would eliminate many of the opportunities for delaying elections that unions say give employers more time to threaten workers against organizing. Unions say the existing rules are tilted in favor of employers, helping to explain why union membership in the private sector has plummeted from 36 percent in the early 1950s to 7 percent today.

Employer representatives told the labor board that streamlining the election process would deprive employers, especially small businesses not versed in labor law, of the chance to consult with lawyers and communicate with their workers prior to a vote.

“It is patently unfair to make it virtually impossible for an employer to present the other side of the organizers’ pitch,” said Brett McMahon, a vice president of Miller and Long Construction, a large nonunion contractor in the Washington area. “What is to fear from a fully engaged presentation of the facts from the employer’s perspective?”

Union representatives countered that employers have ample opportunity to communicate with their workers and noted that the purpose of the 1935 National Labor Relations Act was to give workers a voice with their bosses, not vice versa.

“The board processes as they exist today have become hijacked by the employers,” said Margaret McCann, representing the American Federation of State, County and Municipal Employees. “How has it become that the election process has been subsumed by the employer’s right to communicate with its employees?”

The proposal by the board, which has a majority of Democratic appointees, represents the biggest change to election rules in several decades. But it falls well short of the legislative overhaul — the Employee Free Choice Act — that unions were hoping for with Barack Obama’s 2008 election.

In addition to speeding up elections, that bill would have required mediation when employers and unions failed to agree to a contract and would have allowed workers to organize by getting a majority to sign pro-union cards, without holding an election.

The bill stalled after failing to win a filibuster-proof Senate majority, a shortfall that some union leaders blamed on the lack of a vigorous White House push.

The proposed rules would, among other things, postpone until after elections many employers’ challenges that certain workers are supervisors and ineligible to join a union; remove a 25-30 day waiting period, allowing either side to request reviews, requests that are now rarely filed or granted; and require employers to include cell phone numbers and e-mail addresses in the employee lists they provide organizers.

Taken together, the rules could conceivably shorten the period between a petition filing and election to as little as 10 days, from a median wait of 38 days.

Lawyers representing employers conceded during the debate over the Employee Free Choice Act that labor laws were outdated, but said this was better addressed by revising regulations. But they argue now that the status quo is working, noting that more than 60 percent of elections result in union victories.

Unions counter that many organizing drives fall short of elections because workers fear reprisal. The number of elections has plunged by 80 percent since 1970 — an era, unions note, that has coincided with stagnant wages and a rise in income inequality.

The hearings conclude Tuesday, and the board will take comments until late August.