Some GM investors want to stop a share buyback.

The institutional investors said they are studying ways to keep General Motors from spending $750 million to buy back GM shares held by H. Ross Perot and three other top executives of Electronic Data Systems Corp. In exchange for the buyout, Perot resigned as chairman and chief executive of EDS. The company was purchased by GM two years ago for $2.5 billion. Perot, GM’s largest stockholder, also resigned from GM’s board of directors. GM announced that it would pay about $60 per share, more than double the current market value, for the Class E stock.