The signatories include 34 members of the European Parliament as well as a large part of Parliamentarians for Global Action (PGA) Board and International Council leaders, who represent the entire membership.
The Appeal is still open for new signatories on http://www.pgaction.org/news/release-sheikh-ali-salman.html.
The demand came after Bahrain Public Prosecutor's Office extended for an unlimited period the detention of Sheikh Salman.
Salman was arrested in late December 2014 over alleged anti-regime incitements.
The 49-year-old cleric is charged with “promoting regime change by force, threats, and illegal means, and of insulting the Interior Ministry publicly,” said Bahraini prosecutor Nayef Mahmud.
Tensions have been running high in the monarchy since Salman’s arrest.