In the matter of Sackett v. Environmental Protection Agency, the main issue in this case was:

a. whether the Sackett’s proposed use of their property was in compliance with the Clean Air Act.
b. whether the EPA deprived the Sacketts of their property without due process of law.
c. whether the Sackett’s property contained navigable waters.
d. whether a compliance order of the EPA is final agency action for which there is no adequate remedy at law.

b. whether the EPA deprived the Sacketts of their property without due process of law.

In the matter of Sackett v. Environmental Protection Agency, the main issue in this case was:

d. whether a compliance order of the EPA is final agency action for which there is no adequate remedy at law.

To determine the main issue in the case of Sackett v. Environmental Protection Agency, we need to understand the background of the case and the arguments made by both parties involved.

In this case, Jesse and Lois Sackett, the petitioners, owned a residential lot in Idaho near a lake. They began filling the lot with soil and rocks to build a house, but the Environmental Protection Agency (EPA) issued a compliance order, alleging that the property contained wetlands regulated under the Clean Water Act. The compliance order required the Sacketts to stop all construction activities, remove the fill material, and restore the property to its original condition.

The Sacketts argued that the EPA's compliance order deprived them of their property without due process of law, violating their rights under the Fifth Amendment of the U.S. Constitution. They claimed that they should have the opportunity to contest the EPA's determination that their property contained wetlands before being subject to costly and burdensome requirements.

Based on the information provided, the main issue in this case was:

b. whether the EPA deprived the Sacketts of their property without due process of law.

The Sacketts argued that the compliance order constituted a final agency action, and they had no adequate remedy at law to challenge the EPA's determination. The question of whether the compliance order was a final agency action was crucial to determining whether the Sacketts could seek judicial review.

In March 2012, the U.S. Supreme Court ruled in favor of the Sacketts, holding that the compliance order issued by the EPA could be challenged in court. The Court found that the compliance order constituted final agency action and violated the Sacketts' due process rights. This decision clarified the rights of property owners to challenge EPA compliance orders before they are subject to penalties and enforcement actions.