Unlike an FBI request to talk, a grand jury subpoena carries legal penalties for non-cooperation. Grand juries are used to strip you of your rights. In grand juries, you have no right to remain silent, no right to legal representation (although you can consult with a lawyer after every question), and no right to a trial should you be jailed. In fact, you can be jailed for up to 18 months without ever being charged with a crime.
When you enter the grand jury, you will be asked seemingly innocent questions followed by a series of "who did it" type of questions, which you are forced to answer. "I don't know" is not the correct answer, so you may then proceed to declare the Fifth Amendment, only for it to be stripped away.
The judge will then grant you immunity, and nothing you say can be used against you in a criminal case, BUT it can be used against you in a civil case and against others activists. (This enables prosecuters to get around your Fifth amendment right , which allows you to keep from compulsory self-incrimination).
Once you are granted immunity, you HAVE to talk or you will be held in contempt and jailed for the remainder of the grand jury, which lasts 18 months!
More....
This process has been munipulated to turn the grand jury into an instrument of political repression. Frustrated by the consistent refusal of trial juries to convict on charges of political crimes, the FBI and the U.S. Justice Department convened over 100 grandjuries in the late 1960's and subpoenaed more than 1,000 activist from the Black, Puerto Rican, student, women's, and anti-war movements. Pursuit of fugitives and alleged terrorists was the usual pretext. MAny targts were so terrified that they dropped out of political activity. Others were jailed for contempt of court without any criminal charge or trial!!
ENDNOTES 1. Grand juries were first established as a shield against governent oppression on citizens. This meaning that the grand jury was used to keep the government from charging innocent citizens with outrageous crimes.
2. Due to the informaiton above, England does not use grand juries anymore.
In short, it is very smart to NOTcooperate with grand juries because ANYTHING YOU SAY - ANYTHING - gives them information, which is want they want.