Troops would get a 2.1 percent pay raise in 2018 under a Senate bill approved late Monday, but married military couples with dependents would potentially lose hundreds of dollars a month due to a new cap on housing allowances.

The upper chamber of Congress approved its version of the $700 billion defense authorization act by a vote of 89-8.

The 1,215-page bill now heads to closed-door negotiations with House lawmakers known as "conference," in which the two versions of the annual policy bill will be combined.

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A final version of the legislation will be sent to President Donald Trump for his approval later this year.

Trump has supported a 2.1 percent pay raise for troops -- 0.3 percentage point lower than the 2.4 percent passed by the House.

Proposed BAH Cut

The Senate's version would cap the amount of housing allowance dual-military couples with dependents can receive.

Currently in those cases, the higher-ranking spouse receives that allowance at the with-dependents rate, while the lower-ranking spouse receives it at the without-dependents rate. The Senate proposal would instead require that both receive the without-dependents rate. As a result, affected troops could see several hundred dollars less in their paychecks per month.

Officials estimate that the change to the housing allowance benefit could save the Pentagon about $52 million in fiscal 2018, which starts Oct. 1.

Prescription Drug Increase

Senate lawmakers also approved an increase to the cost of prescription drugs for all Tricare users except active-duty troops.

Currently, a 30-day supply of generic drugs is $10 at an in-network retail pharmacy, while the cost of a 30-day supply of brand-name drugs is $24. A 90-day supply of generic drugs ordered through the by-mail home delivery program is free, while a 90-day brand-name supply is $20.

Under the plan approved by the Senate, those costs would go up by 2026 to $14 for a 30-day supply of a generic drug and $45 for a 30-day supply of a brand-name drug at an in-network retail pharmacy, while 90-day supplies of generic and brand-name drugs from the mail-order system would be $14 and $45, respectively.

-- Amy Bushatz can be reached at amy.bushatz@military.com. Follow her on Twitter at @amybushatz.