The word has two uses. In a gurdwara, the hukamnama is the passage read at random from the Guru Granth Sahib Ji, opened at a page, and taken as the instruction for the day. The one read at the Golden Temple each morning is published and circulated worldwide.
The second use is institutional. A hukamnama issued from the Akal Takht is an edict binding on the Panth. Historically these were letters from the Gurus to sangats, and a number of originals survive with the Gurus' signatures.
Hukamnamas from the Akal Takht in the modern period have excommunicated individuals, settled ritual questions, and directed political action. Their authority depends on the standing of the jathedar who issues them, and jathedars are appointed by the SGPC, which is an elected political body.
That circularity, a religious authority appointed by a body elected on party lines, is the central problem of Sikh institutional life and it has produced repeated crises, including hukamnamas being issued, withdrawn and contradicted.
The surviving Guru-period hukamnamas are among the most important Sikh documents in existence and many are in private hands.
The one at Amritsar is taken before dawn, written up, translated and posted, and it reaches phones in Vancouver and Southall before the working day starts there. A practice built on a book being opened at random in one room is now a daily broadcast on four continents.
About ninety hukamnamas of the Guru period are known, on paper under a seal, addressed to sangats at Patna, Dhaka, Kabul and across the Malwa. Ganda Singh collected and published them in 1967 and that is the edition everybody works from, and originals still surface in family collections.
A jathedar can be removed by the committee that appointed him. That sentence contains the whole of the problem, and every crisis of Sikh institutional authority in the last fifty years has been a version of it.
Akal Takht records of modern hukamnamas.