Supreme Court justices seemed reluctant Wednesday to disallow a type of agreement between employers and unions that has become increasingly important to the labor movement as it tries to grow its ranks.

The case involves neutrality agreements, which a union lawyer told the court are commonly used in organizing hotel and casino workers.

Under such an agreement, an employer might remain neutral during the organizing campaign and even grant the union access to company grounds or lists of employees. In return, the union might agree to give up the right to strike or throw its support to a matter important to the company.

“Many employers and unions find agreements such as this useful to avoid conflict during organizing campaigns,” lawyer Richard G. McCracken told the court at Wednesday’s arguments. He represents Unite Here, a union seeking to represent employees of a Hollywood, Fla., greyhound track and casino.

“They are efficient. They avoid the hard feelings that come in many contested organizing campaigns and thereby create a good environment for collective bargaining,” McCracken said.

But some business organizations and right-to-work groups say businesses often are bullied into entering into such agreements. The case before the court resulted from a lawsuit brought by Martin Mulhall, who worked for the Florida company Mardi Gras Gaming.

While other federal appeals courts have upheld such agreements, the U.S. Court of Appeals for the 11th Circuit said the neutrality agreement at issue violated a section of the Labor Management Relations Act. It forbids an employer to “pay, lend, or deliver . . . any money or other thing of value” to a labor union seeking to organize the company’s workers.

In this case, the casino allowed the union access to its employees and agreed to election rules allowing employees to vote by checking a card in front of others rather than by secret ballot. The union made concessions as well and also agreed to spend $100,000 to support a 2006 referendum to allow slot machines at the casino.

The labor act bans employer payments to unions to discourage bribes and corruption. McCracken argued that the “thing of value” language wasn’t meant to cover what are routine matters of collective bargaining.

Justice Samuel A. Alito Jr. said access to company grounds would seem like a thing of value. And Chief Justice John G. Roberts Jr. said he did not see how the employer’s agreement to a “card-check” election rather than secret ballot could not be seen as a benefit.

“The union organizer comes up to you and says, ‘Well, here’s a card. You can check I want to join the union, or two, I don’t want a union. Which will it be?’ And there’s a bunch of your fellow workers gathered around as you fill out the card,” Roberts said.

Deputy Solicitor General Michael R. Dreeben, arguing for the government on behalf of Unite Here, said the court had decided in previous cases that card-check elections are legitimate.

William L. Messenger, a lawyer for the National Right to Work Legal Defense Foundation representing Mulhall, received tougher questioning.

Messenger said it should be clear that the casino had given the union a thing of value.

“If the employer gives this assistance and the union gives something in return — for example, here the $100,000 political campaign and agreement not to strike — then it becomes a payment, because the consideration shows payment,” he said.

But Justice Ruth Bader Ginsburg said the 11th Circuit’s decision was not that neutrality agreements necessarily violated the law. It wanted a lower court to discern whether the specific agreement was corrupt.

Justice Elena Kagan led Messenger through a series of accommodations she said were accepted practice in labor negotiations that he would find objectionable in a neutrality agreement.

Kagan asked, did he think “the National Labor Relations Act prohibits employers from providing access to their premises, from granting a union a list of employees, or from declaring itself neutral as to a union election”?

When he answered, “Yes, with caveats,” Justice Anthony M. Kennedy asked Messenger if he acknowledged that his answer “is contrary to years of settled practices and understandings.”

Still, both liberal and conservative justices questioned the union’s pledge to spend $100,000 on the slot machine referendum.

“That $100,000 is troubling to me because I think what the circuit was saying is if the $100,000 bought the peaceful recognition provisions, then that’s corrupt, and that is outside the exemptions that the law provides,” said Justice Sonia Sotomayor.

McCracken said the money was not given to Mardi Gras, but spent in an effort to make sure the company was successful and there would be more jobs.

“It was actually the union’s own exercise of its speech and petition rights as it campaigned for the passage of the initiative that would allow the company to get into business in the first place as a casino,” he said.

The case is Unite Here Local 355 v. Mulhall .