TOKYO (Reuters) - Japanese authorities raided the headquarters of a pachinko operator on Thursday as part of a bribery investigation centered on a ruling party lawmaker, media reported, widening a scandal that could undermine government efforts to develop casinos.

The Tokyo-based firm was under investigation for possible ties to ruling party lawmaker Tsukasa Akimoto, who was arrested on Wednesday on suspicion of accepting bribes when he oversaw the government’s policy on casino development, broadcaster NHK said.

Without identifying the pachinko company that was raided, NHK said its accounts were being scrutinized for any transactions involving Akimoto, who in the past served as a consultant for a firm that had dealings with the pachinko operator.

Pachinko, a slot-cum-pinball form of gambling, is a national obsession though the number of players is declining as younger generations prefer to play games on their mobile phones.

Following Akimoto’s high-profile arrest, media has reported that prosecutors have been expanding their investigation into whether he accepted cash and gifts from 500.com, an online gambling operator based in China interested in developing a casino in Japan.

Prosecutors have not named the company.

While Japan’s top government spokesman insisted that Akimoto’s arrest would not delay government plans to develop three casino resorts, the investigation will likely raise questions about the bidding process.

Laws to legalize casinos in Japan have been met with public opposition because of concern about gambling addiction.

Akimoto is accused of receiving about 3 million yen in cash and a family holiday from officials at 500.com’s Japanese subsidiary, according to media reports. He has denied any wrongdoing.

The company has not responded to multiple requests for comment.

Prosecutors have arrested three other people suspected of bribery and raided the offices of a former member of parliament for the ruling Liberal Democratic Party (LDP), Shigeaki Katsunuma, and current LDP lawmaker Takaki Shirasuka in connection with the case, media reported.

Las Vegas-style casino resorts are among Prime Minster Shinzo Abe’s plans to attract foreign tourists.

Japan, which has a shrinking population and economy, is desperate to maintain growth in tourism, particularly after the Tokyo Olympics next year.

Some analysts have said the casino market could be worth about $20 billion a year or more, thanks to an affluent population and the proximity to Asia’s wealthy gamblers.

Analysts say that Akimoto’s arrest may add to the negative images that many Japanese people have of casinos, and also weigh on Prime Minister Shinzo Abe, who is fighting allegations of using party funds to entertain supporters, which has hit his public approval rating.