Plenty of companies at various times have shareholder agreements that make it a breach of contract to sell shares, or that regulate conditions under which you can be dragged along on a sale on terms you have no say in. It affects risk, and so will affect your ability to raise funds on those terms but structuring it ways that allows the company to buy back but ensures an investor or lender with shares as security will get sufficient profit potential to outweigh the risk is still entirely possible.