FILE PHOTO: A patient undergoes an eye exam at the Remote Area Medical (RAM) health clinic in Inglewood, California August 11, 2009. REUTERS/Mario Anzuoni

WASHINGTON (Reuters) - Four U.S. senators expressed concern on Wednesday that federal employees affected by the partial government shutdown could lose their dental and vision health insurance benefits if they are unable to pay their premiums.

In a letter to the government’s Office of Personnel Management (OPM), Democratic Senators Mark Warner, Tim Kaine, Chris Van Hollen and Ben Cardin said forcing workers to pay the premiums during the shutdown would be “unacceptable.”

Some 800,000 federal employees have been furloughed or are working without pay since the shutdown began on Dec. 22, after Republican President Donald Trump and Democrats in Congress deadlocked over his demand for $5.7 billion for a border wall with Mexico.

With no paychecks and thus no payroll deductions, federal workers subject to the shutdown will miss paying their vision and dental premiums. OPM has said workers would start receiving bills for the premiums depending on how long the shutdown lasts.

“We are alarmed that unpaid federal employees will be required to incur this additional financial hardship during a time when they can least afford it,” the senators said.

The senators said some insurers were willing to allow workers to continue coverage without payment and urged OPM to work with all insurers to help employees maintain their coverage.

The states the senators represent - Virginia for Warner and Kaine and Maryland for Cardin and Van Hollen - have a large population of federal workers. Many of those affected by the shutdown have turned to unemployment assistance, food banks and other support, or have sought new jobs.

OPM did not immediately respond to requests for comment.