unique constraint on more than one tables

Hi,

Imagine I have two tables, like this:

create table bla_a (
  id serial primary key,
  name varchar(31) not null,
  comment varchar(31)
);

create table bla_b (
  id serial primary key,
  name varchar(31) not null,
  blabla int
);

I want to make sure that both tables could not have the same value for
name column. Can I do that?

insert into bla_a ( id, name, comment ) values ( 1, 'bo', 'ha');
insert into bla_b ( id, name, comment ) values ( 1, 'bo', 3);

I want to make the second insertion failed because of unique
constraint. Can I do that?