Why do big businesses want Britain to stay in the EU?

Many US big firms including Goldman Sachs, JPMorgan, are paying 6-figure contribution to support the Britain Stronger in Europe campaign. One senior US investment banker was precise to describe the reason why the big businesses do not want Britain to leave the EU, "every single contract will have to be renegotiated - that means every credit default swap, every derivative, every loan agreement. It's a nightmare." However, there are more reasons. If Britain leaves the EU, the costs due to taxes and tariffs will increase. In addition, if the EU workers are no longer eligible to work within the UK, then the cost of providing sponsorship to the EU workers will also add costs to these big firms. Moreover, many of these companies have their head offices in London. If Britain leaves the EU, they may consider to build separate head offices in the European continent,requiring more investment. Therefore, if Britain leaves the EU, these big companies will have higher operation costs.