If you describe something as intolerable, you mean that it is so bad or extreme that no one can bear it or tolerate it. They felt this would put intolerable pressure on them = unbearable tolerable + intolerably in·tol·er·ably intolerably cramped conditions. too difficult, bad, annoying etc for you to accept or deal with tolerable
Not tolerable; not capable of being borne or endured; not proper or right to be allowed; insufferable; insupportable; unbearable; as, intolerable pain; intolerable heat or cold; an intolerable burden