How do variations occur?

The contract usually sets out a procedure for the issuing of instructions for variations.

In practice however, contractual procedures for variations are not always followed. Disputes often arise over whether:

a variation instruction was given in accordance with the contract; or
the contractor has notified a variation claim in accordance with the contract.

If the principal does not follow the procedure for instructing a variation then the contractor may refuse to perform the variation. If the contractor elects to perform a variation which has been incorrectly instructed, then the principal may be entitled to refuse to pay for it under the contract.