Syntax error at or near “on”

Hello!

In PostgreSQL 8.4.13 why do I please get the syntax error

ERROR: syntax error at or near "on"
LINE: ... references balkan_users(id) check (id <> author) on delete ...

for the following 2 statements?

create table balkan_users (
id varchar(32) primary key,
first_name varchar(64) not null,
last_name varchar(64),
female boolean,
avatar varchar(128),
city varchar(64),
mobile varchar(64),
login timestamp default current_timestamp,
logout timestamp,
last_ip inet,
vip timestamp,
mail varchar(256),
green integer,
red integer,
medals integer not null default 0
);

create table balkan_rep (
rep_id serial,
id varchar(32) references balkan_users(id) check (id <>
author) on delete cascade,
author varchar(32) references balkan_users(id) on delete cascade,
author_ip inet,
nice boolean,
about varchar(256),
stamp timestamp default current_timestamp,
primary key(id, author);
);

Thank you!
Alex