AUSTIN — A new digital trove of data showing who is paying to influence elections on Texas airwaves is set to become available ahead of this year's big-money congressional and presidential races.

Starting Friday, more than 175 Texas radio stations could be required to begin publishing documents online in a searchable database detailing political ad buys, the latest attempt by the Obama administration to boost transparency around election spending.

That's because of the expansion this year of a Federal Communications Commission requirement put in place in 2012 for some broadcast television stations to upload political ad buy data online.

The ad buy filings contain key information about who paid for the spot and which candidate is supported or opposed, helping academics, watchdogs, journalists and the public shine a light on outside groups and operatives bankrolling political attack ads.

For now, the online requirement only extends to commercial radio stations with five or more employees in the top 50 markets across the country, which includes San Antonio, Dallas-Fort Worth, Houston and Austin.

The Texas Association of Broadcasters estimates that more than 175 stations in the Lone Star State's four largest markets are preparing in the meantime.

Large satellite and cable operators, including Comcast in Houston, will also have to start putting ad buy documents into the FCC's searchable database starting today. Comcast, in particular, has remained stubborn about making such data available electronically, even while a major rival, Time Warner Cable, voluntarily started doing that several years ago. A Comcast spokesman did not return a request for comment, but watchdog groups applauded the new guidelines.

"Expanding access to information about who is buying political ads is a win for the voters and the public at large," said Jenn Topper of the Sunlight Foundation, a group based in Washington, D.C., that advocates for government transparency.

For decades, anyone interested in seeing political ad buy data would have to go in person to an individual station or cable operator in each city to gain access to the files. TV and radio broadcasters, which use public airwaves to disseminate programming, were required to keep a physical folder of political ad buys open for public inspection.

The FCC has said its goal is to modernize public access to important election spending data.

"By including these services in our transition to an online public file, we continue our effort to harness the efficiencies made possible by digital technology to make public file information more readily available to the public, while at the same time minimizing the burden on covered entities of maintaining the file," the FCC said in a January report ordering the expanded guidelines.

The FCC in 2012 originally required only the top four national networks in the country's 50 largest television markets to upload ad buy documents. The agency expanded the requirement for the rest of the TV markets across the country two years later.

Michael Schneider, vice president of legislative and regulatory affairs for the Texas Association of Broadcasters, said the similar roll-out for radio stations should make the digital transition easier for smaller markets. However, Schneider said he's heard concerns from small stations in big markets that are required to make documents available starting today.

"It's a learning curve, but I think TV demonstrated that stations can rise to the occasion," he said. "The TV stations have seemed to adapted OK."

Most election dollars for ads are spent on TV spots, and an increasing segment of that outlay is being used to target partisan viewers on cable television.

However, radio is a cheaper alternative that remains largely popular among state and local candidates in Texas. Take, for example, the run-up to the 2014 Texas Republican primary, when almost $200,000 in political ads were sold on the station owned by Lt. Gov. Dan Patrick, KSEV in Houston. KSEV is among the stations that will have to start reporting ad buy data online.

Schneider said Texas politicians, including many running in Texas House races, "have come to realize that radio can be a good political ad buy."

"It's an efficient and economical way to make political dollars stretch," he said.