Before visitors to the Metropolitan Museum of Art can stroll past the Picassos, Renoirs, Rembrandts and other priceless works, they must first deal with the posted $25 adult admission and the meaning of the word in smaller type just beneath it: "recommended."

Confusion over what's required to enter one of the world's great museums, which draws more than 6 million visitors a year, is at the heart of a class-action lawsuit this month accusing the New York City institution of scheming to defraud the public into believing the fees are required.

The lawsuit contends that the museum uses misleading marketing and training of cashiers to violate an 1893 New York state law that mandates the public should be admitted for free at least five days and two evenings per week. In exchange, the museum gets annual grants from the city and free rent for its building and land along pricey Fifth Avenue in Central Park.

Met spokesman Harold Holzer denied any deception and said a policy of requiring visitors to pay at least something has been in place for more than four decades. "We are confident that the courts will see through this insupportable nuisance lawsuit."

The suit seeks compensation for museum members and visitors who paid by credit card over the past few years.

"The museum was designed to be open to everyone, without regard to their financial circumstances," said Arnold Weiss, one of two attorneys who filed the lawsuit on behalf of three museum-goers, a New Yorker and two tourists from the Czech Republic. "But instead, the museum has been converted into an elite tourist attraction."

Among the allegations are that third-party websites do not mention the recommended fee and that the museum sells memberships that carry the benefit of free admission, even though the public is already entitled to free admission.

The Metropolitan Museum is one of the world's richest cultural institutions, with a $2.58 billion investment portfolio, and isn't reliant on admissions fees to pay the majority of its bills. Only about 11 percent of the museum's operating expenses were covered by admissions charges in the 2012 fiscal year. As a nonprofit organization, the museum pays no income taxes.

The Met's Holzer said the basis for the lawsuit -- that admission is intended to be free -- is wrong because the state law the plaintiffs cited has been superseded many times and the city approved pay-what-you-wish admissions in 1970.

"The idea that the museum is free to everyone who doesn't wish to pay has not been in force for nearly 40 years," Holzer said, adding, "Yes, you do have to pay something."

New York City's Department of Cultural Affairs agreed to the museum's request in 1970 for a general admission as long as the amount was left up to individuals and that the signage reflected that.

Similar arrangements are in place for other cultural institutions that operate on city-owned land and property and receive support from the city. It's also a model that's been replicated in other cities.

Holzer also noted that in the past fiscal year, 41 percent of visitors to the Met paid the full recommended admission price -- $25 for adults, $17 for seniors and $12 for students.

A random sampling of visitors leaving the museum found that there was a general awareness that "recommended" implied you could pay less than the posted price.

But Dan Larson and his son Jake, visiting the museum last week from Minnesota, were unaware there was any room to negotiate the admission price. They paid the full $25 each for adult tickets.

"My understanding was you pay the recommended price," said Larson, 50. "That's clearly not displayed."

Alexander Kulessa, a 23-year-old university student from Germany, said friends tipped him off about the admission fee.

"They said, `Don't pay $25,"' said Kulessa. "They said it will be written everywhere to pay $25, but you don't have to pay that."

For Colette Leger, a tourist from Toronto, paying the full $25 was worth it.

"It's a beautiful museum, and I was happy to pay," she said.