Der Spiegel is reporting: 
Copenhagen Mayor Ritt Bjerregaard sent postcards to city hotels warning summit guests not to patronize Danish sex workers during the upcoming conference. Now, the prostitutes have struck back, offering free sex to anyone who produces one of the warnings.
Now, according to Wikipedia, 
In Denmark, prostitution itself is legal, but operating brothels and other forms of pimping are illegal activities.. Prostitution was decriminalized on 17 March, 1999, when changes were made in the penal code, but practically it had been tolerated for a long time prior to these changes to the penal code.
The age of consent in Denmark is 15 years, however, for prostitution it is 18 years, and sex with a person below 18 years of age as an act of prostitution is a serious offence.
The traditional center for prostitution in Copenhagen is the district behind the Copenhagen Central Rail Station (Mainly Istedgade, Halmtorvet and SkelbÃ¦kgade), and until recently the number of street prostitutes and sexually oriented businesses in this area was declining. Now street prostitutes – mainly from Eastern Europe and Africa – are growing in numbers. Like many other European cities, many prostitutes now use internet based ads for incall and outcall services.
So, I must in all candor ask why the mayor decided to pick now to make this request. If it the mantra that those who believe in global warming don’t engage is sex? They don’t want those who are spreading the gospel according to Al Gore, to get involved with any trace of what might generate scandal later? I don’t know if that’s the reasoning for the request here, but frankly, I can’t come up with any other scenario that makes any sense at all, can you?