The original treaty put the UN in charge of seabed mining, and allowed them to regulate and tax. It would have mainly taxed Western companies who were able to do seabed mining. Also, it originally required technology transfer and American companies would have to share their tech and patents with the whole world. After the collapse of the USSR the US pushed for the treaty to be amended to limit taxation, remove the tech Transfer, and guarantee the US a veto if they joined.

The amendment was enough to convince the W Bush admin to join the treaty, and the ratification process was started in the Senate, but basically what happened is Obama became president and supported it so the Republican Party torpedoed the treaty just to cause disruption.