Univision’s O&O stations in New York, Los Angeles, Dallas, and other big markets went dark on Charter Communications cable systems Tuesday at midnight, escalating a carriage dispute between the companies that has already sparked a lawsuit.

Univision pulled its station signals from Charter systems after what it said was Charter’s failure to engage with “repeated, good-faith efforts to reach an agreement.”

But Charter has maintained that it already has a long-term contract in force with Univision. The dispute stems from Charter’s acquisition last year of Time Warner Cable and Bright House Networks, which made it the nation’s second-largest cable operator behind Comcast Corp. Univision, the Spanish-language TV giant, sued Charter last July in a dispute involving the post-merger contract terms.

“We have a contract with Univision and we expect them to honor it,” a Charter spokesman said early Wednesday.

Univision accused Charter of abusing its newfound market clout by driving a hard bargain with a network serving Hispanic viewers. Retransmission consent wrangles between TV station owners and MVPDs are common these days, but blackouts of prominent networks in top markets typically draw more attention from regulators and lawmakers, given the number of viewers affected.

“Given the size of the distribution platforms that it controls, Charter has an obligation to its customers to provide them with access to content that is in-language and in-culture, which is vitally important during these politically volatile times,” Univision said in a statement. “This is part of a continuing fight against mega mergers to ensure that there are diverse voices and opportunities for minorities in the media marketplace. Univision’s top priority remains steadfast: providing critical news and information to empower and serve the Hispanic community.”

It’s not clear how many Univision O&Os are in Charter markets, but Charter is the largest cable provider in New York and Los Angeles, and it has a big presence in Texas — all of which are big markets for Spanish-language TV.

The fight boils down to a dispute over which contracts govern Charter’s deals with Univision — the pre-merger contracts that Charter had in force, or the deals that Time Warner Cable had in place at the time of the merger. Time Warner Cable was a much bigger provider than Charter, so it was able to secure more advantageous terms for retransmission consent with Univision. Univision maintains that Charter is in breach of its pre-merger contract because the company has shifted to paying Univision under the more favorable Time Warner Cable terms across the board.

Fox News has a lawsuit pending against Charter on similar grounds.

The showdown with Univision is turning into the first big public relations battle for Charter since it vaulted into the top echelon of MVPDs. Charter at present has about 17 million video subscribers. The disruption in service for Univision on Charter systems could be politically touchy for the company at a time when there is heightened attention to diversity and inclusion in the media and cultural landscape.

The Univision-Charter row, if protracted, could also be an early test for newly appointed FCC chairman Ajit Pai. In 2015 Pai’s predecessor, Tom Wheeler, brought his power of persuasion to bear in a retrans fight between Sinclair Broadcast Group and Dish Network. Pai in the past has advocated that the commission play a very limited role in referring such disputes.