Travelers frustrated by long security lines may not see immediate relief, even as Transportation Security Administration officers begin receiving pay again on Monday after working without wages for more than a month during the partial government shutdown.

President Donald Trump signed an executive order Thursday directing federal officials to ensure that TSA workers are paid despite the shutdown, breaking a more than 40-day stretch in which officers went without salaries.

But the move is unlikely to bring instant relief at airport checkpoints, according to former TSA Administrator John S. Pistole.

“It’s a temporary fix,” he told NBC News. The more pertinent question, he said, is how many workers actually return to their posts now that paychecks are set to resume Monday.

More than 500 officers have quit during the shutdown, according to the Department of Homeland Security, while thousands more have called out because they can’t afford basic expenses.

TSA callout rates reached a high of 12.35% of the workforce on Friday, accounting for more than 3,560 employees, a DHS spokesperson said Saturday. The department added that at Trump’s direction and under Homeland Security Secretary Markwayne Mullin, TSA has “immediately begun the process of paying its workforce” and that officers “should begin seeing paychecks as early as Monday, March 30.”

Those shortages have forced travelers to contend with missed and canceled flights, long security lines and growing uncertainty around air travel.

If most officers report back beginning Monday and airports are able to restore staffing, wait times could start to ease within several days to a couple of weeks, Pistole said.

“It really depends on that asterisk of how many people show up,” he said.

Some workers who left may already have other jobs lined up, raising questions about whether some will return at all.

“How many of them come back after they get this paycheck? Or maybe they already have another full-time job lined up, they’re just waiting to inform TSA after they get their check on Monday,” Pistole said. “So there are a number of variables there.”

Pistole said the uncertainty, coupled with TSA’s typical annual attrition rate of about 7%, could mean delays will continue even after pay resumes.

Until then, some travelers may want to consider alternatives such as driving, rail or bus.

“I think many will and are looking at those options to say, ‘Is that more reliable? Because the last thing I want to do is get to Bush International Airport in Houston and have a four-hour wait,’” Pistole said.