Consideration Given for New contracts

Hello,
We are looking at having all of our employees sign updated contracts as ours are currently outdated and inconsistent. From what I understand, there needs to be a form of consideration given for an employee to sign a new contract. Do you know if we could simply have employees sign at raise time and that would be the consideration? Each year our employees receive an increase in March, so we were hoping to have them re-sign then with new salaries. But I was not sure if an annual increase would not be considered consideration.