In their letter, the senators said they would also oppose any measure "that would eliminate or weaken the Hyde Amendment or any other current-law pro-life protections, or otherwise undermine existing Federal pro-life policy."
Notably, Sen. Joe Manchin (D-W.Va.) did not sign the letter. He vocally supported the Hyde Amendment in December, in an interview with National Review, and said he would vote against legislation repealing it.
Manchin, who is endorsed by Democrats for Life of America, is considered a key vote in the Senate with Democrats and Republicans both holding 50 seats. Some pro-life groups, however, have expressed caution over Manchin's reliability as a critical pro0
Daines' group of 47 senators would constitute a filibuster-proof majority in the Senate, able to thwart passage of pro-abortion legislation. The filibuster is a parliamentary procedure that requires 60 votes to end debate and move a bill for consideration by the full chamber.
However, Democrats have said they will use the procedure of "reconciliation" to pass budget-related items; this procedure only requires a simple majority to pass a budget-related measure.
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Daines told CNA last week that he is concerned Democrats could use reconciliation to pass a funding bill that does not include Hyde Amendment protections.
The Senate letter follows a similar effort in the House. On Jan. 26, nearly 200 House Republicans signed a letter upholding the Hyde Amendment and other pro-life budget riders that prohibit taxpayer funding of abortions.
The letter was endorsed by pro-life groups including the USCCB, Susan B. Anthony List, March for Life, Americans United for Life, and Live Action.