The House of Representatives is requiring all lawmakers to wear masks once again as COVID-19 cases rise nationwide driven by the highly contagious delta variant.

The move comes one day after the Centers for Disease Control and Prevention revised its guidance to recommend that fully vaccinated Americans wear masks indoors in parts of the U.S. where COVID-19 is surging, notably in areas classified as having "substantial" and "high" transmission of the coronavirus, as noted by county level on the CDC's website.

In an email, Dr. Brian P. Monahan, the attending physician of the United States Congress, reinstituted the mask mandate on the House side of Congress, urging all congressional lawmakers and staff to wear a "well-fitted, medical-grade filtration face masks."

“For the Congress, representing a collection of individuals traveling weekly from various risk areas (both high and low rates of disease transmission), all individuals should wear a well-fitted, medical-grade filtration mask (for example an ear loop surgical mask or a KN95 mask) when they are in an interior space,” Monahan wrote.

Monahan urged Senate lawmakers and staff to follow the same advice, but stopped short of putting a mask mandate in place. The Senate did not previously have a mask requirement.

On the House floor Wednesday, Speaker Nancy Pelosi reminded her colleagues that there could be consequences to not following the mask rules.

"Members are reminded that under House Resolution 38, the sergeant-at-arms is authorized and directed to impose a fine against any member acting in violation of this policy," Pelosi said. "The chair appreciates the continued attention of all members and staff to these house and safety protocols particularly in this changing health environment."

The House lifted its mask mandate June 11. Prior to then, several House Republicans had criticized the policy, especially the longer it lasted. Three members were fined $500 for violating the rule, and at least seven others were issued warnings. 

Early indications were that Republicans will not quietly comply with the reimplemented mandate, either. 

“Make no mistake—The threat of bringing masks back is not a decision based on science, but a decision conjured up by liberal government officials who want to continue to live in a perpetual pandemic state,” tweeted House Minority Leader Kevin McCarthy, R-Calif.

Asked about McCarthy’s comment during her news conference Wednesday, Pelosi answered, “He’s such a moron.”

Pelosi noted that the recommendation came from a doctor and was science-based.

Meanwhile, masks are returning to the White House as well. According to The New York Times, White House staff was informed shortly after the CDC’s announcement Tuesday that they must wear masks when on campus regardless of their vaccination status. 

In response, the White House Correspondent's Association informed reporters that they, too, must mask up at the White House. A sign outside the press area Wednesday reminded them of the new policy.