SEC Market Data Proposal Flouts Constitution, Nasdaq Says

An SEC plan intended to improve stock exchanges’ public data feeds would die in the courts if the agency adopts it, according to Nasdaq Inc.

The proposal, which has securities industry support, aims to make exchanges’ private and public streams for market data more comparable. Traders have come to depend on expensive private feeds with depth-of-book data, detailed auction information, and other records. The plan would add more of that data to the public feeds, which only have basic price information and other core market details.

But the Securities and Exchange Commission would violate the U.S. Constitution’s Takings Clause ...