Nasa is facing an extraordinary backlash from US researchers after it emerged that the space agency has banned Chinese scientists, including those working at US institutions, from a conference on grounds of national security.
Nasa officials rejected applications from Chinese nationals who hoped to attend the meeting at the agency's Ames research centre in California next month citing a law, passed in March, which prohibits anyone from China setting foot in a Nasa building.
The law is part of a broad and aggressive move initiated by congressman Frank Wolf, chair of the House appropriations committee, which has jurisdiction over Nasa. It aims to restrict the foreign nationals' access to Nasa facilities, ostensibly to counter espionage.
But the ban has angered many US scientists who say Chinese students and researchers in their labs are being discriminated against. A growing number of US scientists have now decided to boycott the meeting in protest, with senior academics withdrawing individually, or pulling out their entire research groups.
The conference is being held for US and international teams who work on Nasa's Kepler space telescope programme, which has been searching the cosmos for signs of planets beyond our solar system. The meeting is the most important event in the academic calendar for scientists who specialise in the field.
Alan Boss, co-organiser of the Kepler conference, refused to discuss the issue, but said: "This is not science, it's politics unfortunately."