HARRISBURG -- Amid an investigation into claims that Lt. Gov. Mike Stack and his wife repeatedly mistreated state employees, Gov. Wolf on Friday abruptly yanked the state police detail assigned to his second-in-command and scaled back staffing at the Stacks' taxpayer-funded residence.

The move, one with no recent parallel in Harrisburg, means the lieutenant governor and his wife immediately lose a perk that had been in place for decades -- being escorted by troopers and chauffeured in a state-police SUV equipped with emergency lights. Housekeepers and state maintenance employees will now arrive at their home near Fort Indiantown Gap only at prearranged times and will work under supervision.

Wolf personally delivered the news to Stack on Friday, according to the governor's spokesman. The eight-line letter he gave him did not explain the reasons behind the step.

"I do not delight in this decision, but I believe it is a necessary step to protect commonwealth employees," the governor wrote.

The move comes amid a state inspector general's investigation, requested by Wolf, into complaints that Stack and his wife, Tonya, repeatedly verbally abused members of the state police detail that protected them and staffers at the lieutenant governor's residence.

It is not clear when the probe by Inspector General Bruce Beemer will be completed or if its results will be made public. By revoking Stack's police protection, the governor seemed to signal the information he has received could be troubling.

In a statement Friday night, Stack said he concurred with Wolf's decision.

"I recognize, as does my wife, that certain behavior while dealing with the staff of the lieutenant governor's residence and the Pennsylvania State Police Executive Detail who protects us, is unacceptable and were symptoms of a larger problem," his statement said. "Today, in meeting with Gov. Wolf, I apologized directly to him for any embarrassment this situation has caused, discussed with him some of the reasons for what has occurred, and reiterated our commitment to addressing the causes forcefully and fully."

Still, the move opened a dramatic front in a simmering -- if not publicly known -- rift between the state's two top Democrats, men ostensibly expected to run as a team next year.

They ran as a ticket in November 2014. But Wolf did not choose Stack, a 53-year-old state senator from Northeast Philadelphia, as his running mate -- and their relationship has been distant and chilly, according to sources.

After news of the probe surfaced last week, Stack apologized and pledged that he and his wife would try harder. He did not specifically say what behavior he was apologizing for, only that he sometimes gets stressed and snaps "in anger and frustration." He called such an outburst a "Stack moment."

Sources have confirmed that before requesting the formal inquiry, Wolf's office repeatedly warned the lieutenant governor that there were complaints about his and his wife's behavior. And in an interview, Wolf said he also had personally warned Stack.

Pennsylvania has offered its highest elected officials a police detail since the early 1940s. Like many states, it provides escorts and protection 24 hours a day, seven days a week. The duties include transporting the governor and lieutenant governor, and surveying and securing places where they are scheduled to appear. They also provide security at the governor's and lieutenant governor's residences.

For the lieutenant governor, that protection has been provided as a courtesy, according to Wolf's office.

In the 2015-16 fiscal year, the state spent $5.2 million on the state police Executive Detail, which protects the Wolfs and the Stacks, according to a legislative study released this year.

The Inquirer and Daily News and the Pittsburgh Post-Gazette reported this week that Stack spent roughly $19,000 in travel and other expenses in his first two years in office. That figure does not include airfare for state-funded trips he took to destinations within and outside of Pennsylvania.

About $4,200 of that money was billed for overnight stays in Philadelphia hotels at a point when Stack and his wife still owned their house in the city. Most of the trips were described as business trips to attend events or meet with constituents.

The Wolf administration pressed Stack to repay about $1,800 in expenses, apparently concerned that they conflicted with state policy barring elected officials from hotel stays within 50 miles of their homes. Stack's office did repay the money but defended the expenses, and said the couple had moved all their belongings to the Fort Indiantown Gap property right after his 2015 inauguration, and considered it to be their residence. They didn't sell the property until February 2016, records show.

Questions about state police protection have risen before. During Gov. Tom Corbett's administration, troopers routinely escorted Lt. Gov. Jim Cawley's wife to New York City, where she worked. But the Cawleys halted the detail, making the move to cut back on expenses, state officials said at the time.