On April 19, 1529 six Fürsten (princes) and 14 Imperial Free Cities, representing the Protestant minority, petitioned the Reichstag at Speyer against the Reichsacht (Imperial Ban) against Martin Luther, as well as the proscription of his works and teachings, and called for the unhindered spread of evangelical belief.
Barely three years after the Reichstag of 1526, on the 1st March 1529 Charles V announced a new Reichstag. He again let himself be represented by his brother Ferdinand, as he could not personally appear due to the war with France.
In his opening address Ferdinand gave the decision of the Emperor: the annulment of the Reichstag's decision in 1526, recognition of "great mistakes and misunderstanding" and the threat of Imperial Ban against "seduction by false beliefs". Until clarification from another council all further new developments would remain forbidden. He also made further declarations:
''"Those that until now have followed the Edict of Worms should continue to do so. In the areas where this has been deviated from, there shall be no further new developments and no-one shall be refused Mass. Finally, the sects which contradict the sacrament of the true body and blood, shall absolutely not be tolerated, no more than the Anabaptists."
On 19 April the majority of representatives accepted the revocation of the 1526 edict. The evangelicals were told that they should yield "to the fair and proper decisions" of the majority. At this point the evangelical princes left the hall. When they returned somewhat later, Ferdinand wanted to leave the hall and refused to listen to them. So their objection was read out: they protested against the decision of the majority, to undo the decision of the 1526 Reichstag. Ferdinand demanded that they "accepted and obeyed the decision".
The Protestant delegates refused to be bound by secular authority in matters of faith. On 20 April they presented the "Letter of Protestation", which Ferdinand refused to accept. Therefore it did not come to be read out, but was printed and made public.
The "Letter of Protestation" was signed by Johann, Elector of Saxony, Georg, Margrave of Brandenburg, Ernst, Duke of Braunschweig-Lüneburg, Philipp, Landgrave of Hesse, and Wolfgang, Prince of Anhalt.
At the final sitting of the Reichstag on 24 April the "decision of the Reichstag" was once more read out, but no word was said of the protest by the evangelical princes. In response the councils of the evangelical princes and the agents of the Free Cities met on 25 April and drew up a Instrumentum Appelationis, in which complaints against the decision of the Reichstag were once more summarised. This text was brought to the Holy Roman Emperor by an embassy. Since this Reichstag the adherents of the reform movement became known as "Protestants", and thus the protestation of the Princes and Free Cities has been seen as the birth of Protestantism.