Which factor reveals a lack of financial disclosure under the Family Law Act?

The correct answer highlights a specific instance of non-compliance with the financial disclosure requirements under the Family Law Act. The failure to report tax documents is a critical aspect of financial transparency during divorce or separation proceedings. This documentation is essential because it provides a clear picture of an individual's financial situation, including income, assets, and potential liabilities.

Under the Family Law Act, both parties are expected to provide complete and accurate financial information to ensure fair decisions regarding asset division, spousal support, and child support. When one party fails to report their tax documents, it indicates that they may not be fully disclosing their income or financial resources, which can impede the equitable distribution of property and support obligations.

The other options, while they may involve financial considerations, do not directly pertain to the requirement for financial disclosure. Inability to pay rent, a change in employment status, and disagreements on child custody, while they may reflect on a person's financial condition or marital dynamics, do not specifically demonstrate a lack of compliance with the mandated financial disclosure under the Act. Thus, the failure to provide tax documents is the clearest indicator of a lack of financial transparency in the family law context.