Have to agree with the others, I would immediately be looking for another job. These type of companies employing you for contract work, have absolutely no interest in your well being whatsoever. Cover your back and get some other job's lined up, it would appear as though its only a matter of time before your let go, even if your contracts extended, its only prolonging the inevitable.
I would be worried if I were you, I'm in a permanent posting and I'm still worried! never become complacent. As Sarnie says, look out for number one.