Final answer:
Married taxpayers who file jointly cannot switch to separate returns after the tax filing deadline; this is indeed true. This rule prevents couples from choosing the most beneficial filing status retroactively.
Step-by-step explanation:
The statement is true: Married taxpayers who file a joint return cannot later switch to filing separate returns after the filing due date for that tax year. Once the deadline for filing taxes has passed, if a couple has filed jointly, they are no longer able to amend their filing status to file separately for that particular year. This rule is designed to prevent couples from choosing a filing status after seeing which would be more beneficial, as filing statuses can affect tax rates, deductions, and allowable credits.