******** PENDING TRANSACTIONS!!

If have had a problem with money being taken out of my account on random days leaving me with a negative balance. I SEE THERE ARE OTHER PEOPLE WHO HAVE EXPERIENCED THE SAME PROBLEM and all the representatives from the banks keep saying is that it is the merchants who decide when to take their money and it comes without warning or authorization as we are under the impression that it has cleared after the purchases are made. NOW IS THERE NOT A TIME FRAME BY WHICH THESE MERCHANTS MUST CLAIM THAT MONEY, LIKE WITHIN A CERTAIN AMOUNT OF DAYS? I read that if it is not claimed within 7 days it is credited back into your account!! HOW IS WHAT IS HAPPENING HERE LEGAL!!