The Supreme Court refused to halt a proposed investor class-action suit that accuses Blackstone Group of making inadequate disclosures before its 2007 initial public offering.

Investors claim Blackstone CEO Steve Schwarzman knew about problems at two companies in which the private-equity firm had a stake.

The court also turned away a bid by AT&T for a $500 million tax refund in a fight stemming from government subsidies to the company for serving remote areas.