The advertisement could be considered run-of-the-mill these days: Beside the word “Georgi” in bright yellow block letters is a close-up of the backside of a woman wearing a string-bikini. Her skin is dusted with sand, as if she has just risen from a short rest at the beach. A bottle of vodka is superimposed next to her; the word “Georgi” is written in green letters on the bikini bottom.

“Georgi, The First Name In Vodka,” it beckons.

Similar ads are found at beach resorts and in clothing catalogs. Scantily clad women, it is commonly thought, are powerful, albeit blunt, ammunition for companies competing for the youth market.

However, the vodka advertisement was removed from 365 city buses last December for a reason the Metropolitan Transportation Authority’s marketing company, CBS Outdoors, won’t disclose. The company replaced the advertisements with another, almost identical advertisement — instead of the bikini bottom, there is a naked woman who covers herself by crossing her legs and arms.

While the MTA deemed the advertising too risqué for the city’s buses, the Taxi and Limousine Commission decided that it was appropriate for the tops of the city’s yellow cabs. The advertisements have run on 150 yellow cabs since the beginning of the month, and will stay up for at least another week.

Martin Silver, the chief executive officer of Star Industries, which distributes Georgi vodka along with three other brands, said the MTA’s standards curtailed his free speech and ability to sell his product.

“The city didn’t like such a sexy ad, but if you go five blocks in the city you’ll find sexier ads than this one,” he said.

He said the bikini-clad model is his daughter, Laurie Adams, a 36-year-old promotions and advertising manager at Star Industries.

“Best buns in the city,” he said. “Her friends call her ‘buns’ now.”

Ms. Adams echoed her father’s defense of the ad, calling the MTA’s decision “a shame.”

“I just happen to think it’s a great ad,” she said.

Asked what the advertisement communicated to the general public, she said: “It conveys just fun, a good time,” she said, adding “taste” after a moment’s thought. The photo shoot took place at Coney Island, she said.

The owner of Beekman Liquors Inc. on Lexington Avenue, David Frieser, said a liter-sized bottle of Georgi vodka sells for about $10.

“It’s very inexpensive, a sort of a pouring vodka — the kind you use for mixed drinks that don’t call for a specific brand,” he said. On a scale of one to 10, one being the worst in quality, he said it was a two, with rubbing alcohol rating a one.

A spokesman for the MTA, Tom Kelly, said CBS Outdoors manages all advertising on the subways and buses. The MTA sets the ground rules about sensitivity to the city’s communities. If an advertisement is put up that MTA officials believe to be in bad taste, they would ask CBS Outdoors to take it down, he said. Mr. Kelly said the decision to remove the Georgi ad was made by CBS Outdoors.

“We stand behind our original decision in December,” a spokeswoman for CBS Outdoors, Jodi Senese, said in a statement. “We are sensitive to the community’s standards, as our buses travel through every neighborhood in the five boroughs and are viewed by millions of people every day, children included. We do our best to ensure that all our displays are appropriate in the venues in which they are presented.”

A spokesman for the Taxi and Limousine Commission said a marketing company, Clear Channel, handles all of its ads and that no one in the commission exerts any editorial control over them.

“It’s always a case-by-case basis of what someone may think at the time is appropriate or not appropriate,” the chief executive officer of Clear Channel’s Taxi Media Company, Charlie DiToro, said. It is against the company’s policy to comment on specific cases or how it decides if an advertisement is appropriate, he said.

Both advertising companies said they had rejected scores of inappropriate advertisements in the past, but refused to specify what they were advertising.

Although CBS Outdoors refused to point out the specific element of the photograph that it considered inappropriate, a furniture restorer from Cambridge, Mass., who was shown the ad, Devin Mead-Ward, said he had an idea as to why it was banned.

“I would say it’s no worse than anything else I see,” Mr. Mead-Ward, 26, said. “But I think the sand makes it more suggestive sexually.”