The US has the highest corporate tax rate in the world by a good margin. 35% on income (not including state income taxes). The US is one of the few countries that tries to tax the worldwide income of US parents as well. Because of this, the US allows companies to set up foreign subsidiaries and defer income that these subsidiaries earn, provided they meet certain conditions, so that the US owned companies can compete on an equal footing in the countries that they have set up operations with local companies in these jurisdictions that pay the local corporate rates. This profit isn't taxed at the US rate until repatriated.
Sanders wants to eliminate this so US companies will have to pay 35% taxes on income they earn everywhere in the world, even when they are competing against companies in countries where they have a 15% or 20% tax rate. Needless to say, the ability of US companies to compete abroad would be severely handicapped. The local companies can undercut the US company by the difference in the US and local corporate tax rates and maintain the same profit % as the US company.