BOSTON — When it came to business, James "Whitey" Bulger had one basic rule, according to two bookmakers who testified at his racketeering trial Friday: You paid him or you risked getting hurt, or worse.

The bookies described being forced to pay Bulger and his gang monthly fees known as "rent" or "tribute" if they wanted to stay in business. When they or other bookies attempted to go out on their own, they were threatened, both men testified.

Richard O'Brien recalled being summoned to a meeting at a Braintree hotel in the 1970s after one of his agents indicated he wanted to go into business for himself.

O'Brien said Bulger told the man he had another business aside from bookmaking. When the man asked, "What's that?" Bulger replied, "Killing (expletive) like you,'" O'Brien said.

Bulger chuckled in court after O'Brien told the story, a contrast to his usual stoic courtroom demeanor.

Bulger, now 83, is charged in a 32-count racketeering indictment that accuses him of participating in 19 murders in the 1970s and '80s. He is also charged with money-laundering and extorting bookmakers, drug dealers and loan sharks.

O'Brien, now 84, appeared to amuse several jurors who smiled at times as he testified about meeting with gangsters in the 1960s and '70s, including one meeting with New England Mafia boss Raymond Patriarca.

"It was kind of a short meeting because it was the day (Teamsters President) Jimmy Hoffa was arrested, and they were all up in arms about that," O'Brien said.

Another bookie, James Katz, testified that if anyone tried to get away with not paying Bulger's gang, they could "wind up in the hospital."

Katz said he paid $500 to $1,000 a month to the gang.

Katz said he initially refused to testify to a grand jury about the gang's activities after he was indicted in the 1990s because he feared for his safety. But he eventually testified after prosecutors offered him a reduced sentence and entry into the witness protection program.

During cross-examination by Bulger's lawyer, J.W. Carney Jr., Katz acknowledged that he made most of his payments to Bulger's partner, Stephen "The Rifleman" Flemmi, and dealt with other people in the group. He said he only met Bulger once.

Katz was sentenced to four years in prison after pleading guilty to money-laundering, wire fraud and other charges.

After agreeing to cooperate with prosecutors, his sentence was reduced to five years of probation. Prosecutors also vacated a $1 million forfeiture judgment against Katz.

Bulger was one of the FBI's most wanted fugitives after he fled Boston in 1994. He was finally captured in Santa Monica, Calif., in 2011.

In opening statements to the jury on Wednesday, Bulger's lawyer acknowledged that his client made millions by extorting bookmakers, drug dealers and others who ran illegal businesses. But he attacked the credibility of three former Bulger loyalists who are expected to be the prosecution's star witnesses against him, including Flemmi, hitman John Martorano and former Bulger lieutenant Kevin Weeks.

Carney said Flemmi is the one who killed two 26-year-old women Bulger is charged with strangling. He also said Bulger was not responsible for the deaths of two businessmen in Oklahoma and Miami.

Martorano, who admitted killing 20 people and served 12 years in prison, is expected to testify Monday.