More than 1,000 circus employees have rallied in Mexico City, following a ban on using animals in circus activities.
According to the new law, lions, tigers, bears, horses and dogs will not be allowed to perform in circuses.
The law also bans the use of animals in advertisements, prizes, lotteries and many other activities which require what it is described as "a change in the environment, feeding or natural instinct of the animals".
Penalties include fines ranging from $45,000 (£26,811) to $60,000 (£35,748).
The ban does not apply to dolphin shows or bullfighting.
The protesters argued that thousands of people will be left unemployed following the ban.
"Hundreds of families are going to be out of work," clown Julio Cesar Ramirez was quoted by the BBC as saying.
The president of the national circus association, Armando Cedeno, said the measure would affect about 50,000 circus employees and 3,000 to 3,500 animals.
''It is impossible to take these animals back to their natural habitat because they would die,'' Cedeno said.
He added that the animals were treated well.
Isaid Berti, an animal trainer, was quoted by AFP as saying: "We have already demonstrated that we do not harm our animals. They are part of our family!"
He added: "We have watched these animals be born and take care of them their whole lives. How would we abuse them?"
The animal trainer acknowledged that animal abuse does happen in some circuses and suggested an inspection system for the city's estimated 50 circuses.
"Why should those who have done no wrong pay the price for those who have?"
In a press conference, Jesus Sesma, the politician who pushed the law, described it as promoting "a respect for living beings who are not human".
According to Animal Circuses, which aims at educating people about the physical and phsycological suffering of animals in captivity - circuses deny captive-born wild animals their need to exhibit their natural behaviours.
"In a circus, elephants are chained or confined to a small space and are only able to stand up, lie down or shuffle a few paces backwards and forwards," the NGO said.
"Lions and tigers are shut in their beast wagons for over 90% of the time. They, too, need to be able to socialise and roam freely.
"Life in the wild cannot be replicated on the back of transportation trucks or at circus sites around the country."