A trade group that represents 5,500 taxi owners and leases cabs to more than 20,000 hacks has kicked off a $1 million campaign to bring back drivers who left yellow cabs for new options like Uber. The city also recently made it easier for hacks to move back and forth from one section of the industry to another -- such as from driving a black or livery car to a yellow cab.

The campaign by the Metropolitan Taxicab Board of Trade includes 1,500 ads on MTA buses targeting drivers, and ads in local ethnic newspapers that represent twenty countries. It is also spearheading a social media campaign on Facebook.

The ads on the outside of MTA buses say "drive yellow, earn green."

The taxi industry group said that in the past two years, they have seen drivers leave the yellow cab industry, lured by ads suggesting they would make more money with app-based services like Uber, but that many are returning. Many have not earned as much as they expected, the group said.

Because the yellow taxi brand was long iconic of New York City, the industry hasn't had to sell its image in the past, the trade group says.

"However, today, there are other choices for both drivers and for passengers so we need to communicate the clear benefits of both driving yellow and riding yellow -- and that is what the advertising campaign is all about," said its spokesman Michael Woloz.

"We are seeing more and more drivers returning to the industry and in many cases, entering the yellow cab industry for the first time. Yellow is back."

A spokeswoman for Uber declined to comment.

The MTBOT's campaign comes as the Taxi and Limousine Commission recently began letting drivers use one license to drive a yellow cab or a for-hire vehicle, which includes black, livery, and luxury limousine cars. Before, drivers needed separate licenses for the different segments of the industry that are regulated by the TLC.

The agency says the flexibility will be a boon to both drivers and riders, who will have more choices.

"Our goal of increasing mobility between sectors provides benefits for passengers," said TLC Commissioner Meera Joshi in a statement. "But it also applies to drivers, and to that end, the combined medallion/for-hire vehicle license makes it easier for experienced drivers to work across both sectors and reap the economic benefits of options."

The MTBOT's campaign also comes as Uber continues to rapidly grow in New York City. There are more than 27,000 Uber cars on the streets, up from 14,088 in just March of this year.

The app company now has 27 black car bases and one luxury limousine base in New York City. Almost 27,000 cars are now registered to Uber's black car bases, and almost 680 are registered luxury limousines.

There are 13,587 yellow cabs in New York City, according to the TLC. However, taxis tend to be on the streets around the clock, while many Uber drivers only use their cars part-time.

There are also about 7,800 green cabs, which serve the outer boroughs and upper Manhattan, and launched in 2013.

Michael O' Loughlin, of the group Cab Riders United, said he felt the campaign was a good thing for both passengers and drivers.

"Choice is a good thing. It's good customers can choose to have the transportation option that works for them," he said. "In the absence of competition, businesses get lazy or sloppy. It's good to see they're aiming to have the highest standards possible."

Parmjit Singh, 45, is one driver who has applied for the new license, and has driven in the past for a livery car base and a green cab. His wife drives a yellow cab, and he said he wants to try driving a taxi because she was making more money than him. "I am feeling very happy," he said.

The MTBOT has launched a resource center in Long Island City, which has been helping drivers transition from companies like Uber back to yellow cabs, and has created a website called driveyellow.nyc. The center is staffed to help hacks with issues that include traffic tickets and a free defensive driving course.

"Yellow taxi drivers are the lifeblood of this city, and they have one of the toughest jobs in the city," said Jean Barrett, executive director of the group. "Navigating all the regulatory hurdles can be time-consuming, and in some cases confusing."

Kanchas Das, 35, recently began working at the center, and said he has been helping them apply for the new TLC license that would let them work in any section of the industry.

He said he has gotten many calls from interested drivers following an ad in a newspaper for immigrants from Bangladesh.

"Today, we got at least 150," he said on Friday.