The following text is from ICSU(International council for science) booklet in 2008.
Freedoms of scientists
Included in the Principle of Universality above are four specific freedoms for scientists—freedom of
movement, association, expression and communication. Defence of these freedoms is grounded in the
Universal Declaration of Human Rights, particularly Articles 13, 19 and 20. Access to data, information
and research materials for science is also supported by article 27.
Freedom of movement
Problems in obtaining national entry visas are a relatively common obstacle to the freedom of
movement of scientists in various parts of the world. These entry visa issues are most frequently
associated with either security and/or politics and tend to be targeted at particular population groups.
There is also the problem of scientists who are not permitted by their national authorities to travel outside their own countries—generally out of fear that they will reveal embarrassing information about their country or that they might not return. Without careful monitoring and attention, there is a real danger that certain members of the global scientific community will become isolated.
ICSU and visas for scientists
ICSU and its Members have acted when scientists wishing to attend scientific meetings outside their countries of citizenship have been denied visas for political reasons. For example, in the 1970's and 1980's, ICSU actively defended ‘refusenik’ scientists who were denied exit visas from the former Soviet Union (and other Eastern block countries) to attend international scientific meetings with their colleagues in the West. During the 1980's ICSU
intervened on behalf of about 20−30 scientists per year. Examples of difficulties encountered include scientists in Taiwan who were denied visas by mainland China and vice-versa, Chinese scientists who had difficulties obtaining visas to Israel, Iraqis who were denied visas to Sweden and South Korea, Cuban scientists who were denied visas to the US and Australia, and scientists in Israel and South Africa who had difficulties obtaining
visas from a number of countries. ICSU, working with its Members, frequently intervened vis-a-vis the countries
refusing visas and, in the majority of cases, it was successful in reversing the initial refusal.
In some instances, ICSU has called for the relocation or cancellation of scientific conferences when visas have
been denied for political reasons. One notable case occurred in 1988 when ICSU General Assembly was held in China rather than Japan because the Japanese government advised ICSU that South African scientists would not be granted visas.