How does merely a drop below 660 meet the two criteria for freezing a line?
In addition to permitting lenders to reduce or suspend credit limits following a significant decline in a property's value, Regulation Z also permits such actions if the "creditor reasonably believes that the consumer will be unable to fulfill the repayment obligations under the plan because of a material change in the consumer's financial circumstances."8 The Official Interpretations state that two conditions must be met to use this situation as a basis for reducing or suspending a credit limit. First, there must be a "material change" in financial circumstances, for example, a significant decrease in a consumer's income.9 Second, as a result of that material change, the lender must have a "reasonable belief" that the consumer will not be able to meet his or her repayment obligations. Although the Official Interpretations go on to indicate that a lender may –– but need not –– rely on specific evidence, such as a failure to pay other debts, to conclude that a consumer will not be able to pay his or her HELOC obligation, institutions should have a factual basis for any actions taken under this provision. Furthermore, that factual basis should be determined consistently, to avoid the risk of prohibited discrimination or unfair practice.
https://www.fdic.gov/news/news/financial/2008/fil08058a.html