U.S. regulators tightened rules on broadcast owners controlling more than one TV station in a city, and said companies such as Sinclair Broadcast Group Inc. must alter existing arrangements to comply.

The Federal Communications Commission on a 3-to-2 Democrat- led party-line vote Monday, adopted Chairman Tom Wheeler’s proposal to crack down on what he has called attempts to circumvent rules limiting media ownership. The rules are designed to ensure news and information within communities isn’t dominated by one voice.

“Today what we’re doing is closing off what has been a growing end run” around ownership limits, Wheeler said at the FCC’s monthly meeting.

The change adopted attacks a technique in which TV-station owners control the advertising of nearby stations owned by a third party, and reap the sales revenue. The deals position the larger station as “de facto owner” of the smaller station, whose independence is “a legal fiction,” Wheeler said in a March 6 blog post.

Republicans and companies said the arrangements facing new restrictions help fund local programming at struggling television stations in mid-size and smaller markets.

The shared arrangements help stations in smaller markets survive, said Ajit Pai, the agency’s senior Republican. He called the agency’s action “the epitome of arbitrary and capricious decision-making.”

The FCC, by its vote, said shared advertising sales of 15 percent or more amount to common ownership. It gave station owners two years to reduce or cease common ad sales, or obtain a waiver.