The tariff issue had been a point of contention between the North and South for decades starting with the Tariff of 1828. The Morrill Tariff that went before Congress in 1860 was vehemently opposed by the southern states. The tariff issue was also very important to the Union since it provided the major source of tax revenue. In his inaugural address of March 1861, Lincoln practically threatned a military invasion of any state that did not collect its fair share of the federal tariff. In addition, Lincoln issued his Proclamation of Blockade Against Southern Ports in April of 1861 because the tariffs were not able to be collected in the southern states.