Some companies are finding that carbon offsets might not be all that they’re cracked up to be when it comes to building their green image.

They’ve been a convenient way for employers to claim “green-ness.” Have trouble making part of your business “carbon-neutral”? No problem! Buy some carbon offsets.

That was especially the case for long-distance business travel. Jet planes create a large amount of carbon dioxide, a global-warming gas. Whole businesses have been set up to allow companies to purchase carbon offsets to counter the emissions generated by airline flights.

The offsets often fund environmental programs such as planting trees in forests.

But last month, Responsible Travel, a “green travel” company, canceled its offsets program, saying it wasn’t helping to reduce global emissions, according to The New York Times.

Company officials feared that the program might actually encourage some business executives to travel more often.

“The carbon offset has become this magic pill, a kind of get-out-of-jail-free card,” said Justin Francis, managing director of Responsible Travel. Francis says offsets are keeping people from making more significant behavioral changes, like flying less.

It’s proved difficult to monitor the emissions-reduction potential of offsets. There are no industry standards.

Yahoo and the U.S. House of Representatives have also ended their offset-purchase programs.

Paul Dickinson, chief executive of the Carbon Disclosure Project, a large nonprofit consortium of companies that report and reduce their emissions, said rather than buying offsets, he has sharply reduced flying. He’s taking trains or conducting meetings by phone or teleconference instead.