It’s almost Election Day. Shareholders: Do you know how the cash from companies you invest in is being spent to influence the outcomes?

Unless you invest in companies that voluntarily disclose their political spending, the answer is no. Worse, the Securities and Exchange Commission — the presumed guardian of investors’ right to know how corporate executives spend shareholder money — will not lift a finger to help you find out.

The sums in question are not insignificant. Election spending has mushroomed since 2010, when the Supreme Court’s decision in the Citizens United case opened the floodgates to special interest money in politics. The latest tally by the Center for Responsive Politics, a watchdog group, projects that nearly $700 million will be spent this year by groups other than parties and candidates. Of that total, roughly one-third, at least, will be spent by tax-exempt groups, including trade associations and “social welfare” groups that are set up for the purpose of raising money from anonymous donors. Supporters of both political parties use these vehicles, though Republican-backed groups far outstrip Democratic-backed ones in secret fund-raising.

The S.E.C. has a role to play, because a disclosure requirement is the only way for shareholders to know for sure whether and how much the companies they own are donating and whether such spending helps the bottom line. As things stand now, evidence indicates that much of the money flowing to tax-exempt groups comes from companies that give anonymously in order to avoid alienating shareholders, customers or legislators they aim to unseat.