If we've learned anything about telecom regulations over the past 20 years, its that rules can quickly change and that courts often have the last word.

Shares of major TV station owners were falling on Friday after the U.S. Court of Appeals for the District of Columbia stayed a ruling by the Republican-controlled FCC that was to reinstate the so-called UHF discount and aid industry consolidation.

Tegna (TGNA) - Get Report shares on Friday afternoon were off 4.8% and Gray Television (GTN) - Get Report was down 0.6%; Sinclair Broadcast (SGBI) shares were up 0.7% after opening lower.

TV station owners led by Hunts Valley, Md.-based Sinclair protested loudly when former FCC Commissioner Tom Wheeler, an Obama appointee, led a Democratic majority on the commission to eliminate the discount in September. In short, the UHF Discount give TV station owners more room under the federally mandated cap that says that no one company can own stations that reach more than 39% of U.S. households.

By restoring the discount, Sinclair and other station owners would be able to increase their holdings, given that the discount values legacy UHF stations at half their household reach. Wheeler's FCC argued that the discount had become obsolete given the evolution in broadcast technology since the rule was passed in 1986.

The agency reversed course in April under Chairman Ajit Pai, however.

Reinstating the discount is a particularly high priority for Sinclair, which last month secured a deal valued at $6.6 billion to acquire Tribune Media (TRCO) - Get Report , owner of some 36 TV stations around the country, including Chicago's WGN and cable network WGN America.

Sinclair CEO Chris Ripley told investors last month that regardless of whether the UHF discount were eliminated or reinstated, the Tribune Media acquisition would receive regulatory approval. Sinclair announced its acquisition of Tribune three weeks after the Republican majority on the FCC voted to reinstate the discount.

Though regulators could require Sinclair, which owns around 173 local TV stations, to sell some, Pai has indicated he will pursue steps that could lead to raising or even eliminating the 39% household cap.

Still, a group of petitioners including Free Press, Prometheus Radio Project, Media Alliance, Common Cause and the National Hispanic Media Coalition, among others, on May 12 sought court review of the UHF discount decision.

The court determined Thursday that it needed additional time to review the ruling, leaving open the possibility that Pai, a former Verizon attorney who was appointed to the FCC by President Obama in 2012, will succeed in his effort to reinstate the discount, thereby appeasing large TV station owners.

The FCC has filed a brief in support of the reinstatement. Sinclair, 21st Century Fox (FOXA) - Get Report and Ion Media, a privately held TV station group, have done the same.