When I put up this post on the latest developments in UCU, I hadn't seen the legal advice the union had received, and I still haven't. My only source was the email sent to union members. As I read that, the general secretary of UCU is telling the membership that the union's advice is that a boycott call would be illegal, and actively trying to secure opinion in favour of a boycott may also be illegal. In these circumstances the union leadership thinks it unwise to support a debate to this end.
A number of letters in today's Guardian are interpreting the communication as a gag on all discussion of the issues, and on that basis objecting to it. If the interpretation were right, then the objection would also be right. The union does not have this power to stop its members discussing things - they are free to discuss, for example, whether a legal opinion given to their union is compelling, whether the law in some particular or other is morally justified, and therefore whether an academic boycott of Israel should be illegal, if illegal is what it is.
But the letters, if I may say so, are themselves a squawk. Those within UCU who want to discuss these matters not only can do so but ought to know that they can. No communication they've received bars them from it, and the email of a few days ago was probably not intended to do that.