The US is doubling the fine for people who break the rule requiring masks on planes, trains, and other forms of public transit, to slow the spread of COVID-19, with President Joe Biden warning that violators should “be prepared to pay.”

First-time offenders would face a potential fine of $500 to $1,000 and second-time offenders could pay $1,000 to $3,000 under rules that went into effect Friday. The fine previously started at $250 and went up to $1,500 for repeat offenders.

“If you break the rules, be prepared to pay,” Biden said as he announced the increase during a speech outlining sweeping new federal vaccine requirements as part of an effort to increase COVID-19 vaccinations and curb the surging delta variant.

The president also rebuked people who have been taking out their anger about the mask requirement on flight crews.

“And by the way, show some respect,” he said. “The anger you see on television toward flight attendants and others doing their job is wrong. It’s ugly.”

The mask penalties are separate from any civil penalties the Federal Aviation Administration may issue for unruly behaviour.

The mask mandate has been controversial and has led to many tense encounters between passengers who don’t want to wear a mask and flight attendants asked to enforce the rule. The Federal Aviation Administration said last month that airlines have reported 3,889 incidents involving unruly passengers this year, and 2,867 – or 74% – involved refusing to wear a mask.

The rule requiring masks on planes and all public transit will remain in effect until at least Jan. 18 and “as long as necessary” to protect public health amid the pandemic, Department of Homeland Security Secretary Alejandro Mayorkas said.

The mask order, based on Centers for Disease Control and Prevention guidelines for responding to the pandemic, was first issued on Jan. 29, days after Biden took office. Before that, airlines had their own requirements for face coverings, but the Trump administration had declined to make it a federal rule.