Hard Line (Hard Liner)

A “hard line” (also “hard-line” or “hardline”) is an uncompromising set of beliefs. “Hard line” has been cited in print since at least 1949 and possibly was influenced by World War II military language.
 
A “hard liner” (also “hard-liner” or “hardliner”) is someone who maintains a “hard line” and has been cited in print since at least 1960.
 
     
Wiktionary: hardline
Alternative forms
hard line (some consider this to be a misspelling)
Etymology
hard + line
(...)
Adjective
hardline (not comparable)
1.uncompromising; rigidly holding to a set of beliefs
2.(business) belonging to a hardline (business noun sense); e.g. “hardline product”
 
Wiktionary: hard-liner
Alternative forms
hardliner
Etymology
From hard + liner.
Noun
hard-liner (plural hard-liners)
1.A person who takes a firm, uncompromising position on some policy.
 
(Oxford English Dictionary)
hard-line n. attrib. adhering to a hard or firm policy without abatement or concession (cf. sense A. 12c).
1962 Times Lit. Suppl. 21 Dec. 992/5   The ‘hard-line’ periodical Literatura i zhizn, which has up to now dealt exclusively with the literature of the Russian Federation, will close down.
1964 Economist 18 Jan. 206/1   CIA’s‥reputation as a ‘hard-line’ agency.
1965 New Statesman 7 May 710/3   Among those whose toughness stiffened the rebels’ will to resist were‥the 50 or 60 ‘hard line’ communists.
 
hard-liner n.
1963 Sat. Rev. 25 May 22/2   The fact that war has now become an instrument of mutual suicide‥has made no dent in the thinking of hardliners.
1966 Observer 17 Apr. 2/8   Vice-President Humphrey—widely regarded as a hard-liner on Asia.
 
30 May 1949, The Times-Picayune, “Vishinsky’s ‘New Look’: A Report on Limits of Red Geniality” by Nat Barrows, pg. 12, col. 4:
Thus far, the “hard” line continues here.
   
11 February 1950, New York (NY) Times, “Abroad: Of the Making of Policy There Is No End” by Anne O’Hare McCormick, pg. 11:
There is reason to believe that he took the “hard” line, the line dictated by experience, in respect to negotiating with Russia, as a preliminary to a restatement of American foreign policy in general.
 
Google News Archive
9 August 1953, Miami (FL) Daily News, pg. 8B, col. 1:
Malenkov Talk Hints Shift
Back To Stalin’s “Hard Line”
London, Aug. 8—Premier Georgi Malenkov, in one of the most belligerent speeches of his career, appeared today to have switched Soviet foreign policy back into the Stalinist “hard line” against the United States.
 
Google News Archive
6 July 1958, Miami (FL) News, pg. 1B, col. 1:
Hard Line Softens
Just when the score of Americans in Communist hands would be released was problematical, but there were indications that Moscow’s “hard” line of recent weeks was softening.
 
Google News Archive
8 January 1959, Modesto (CA) Bee, pg. B4, col. 2:
Russian Delegate Returns To Hard Line
At Talks On Nuclear Weapons Test Ban
By Robert Korengold
GENEVA—UPI—...
 
Google News Archive
23 December 1959, Pittsburgh (PA) Post-Gazette, “Calling Washington: Everyone Except Ike Got A Prize at Paris Parley” by Marquis Childs, pg. 10, col. 7:
Then the current “soft” President out of the White House there is the prospect that he will be replaced by a President willing to go back to the “hard” line of the cold war.
 
18 March 1960, Portsmouth (OH) Times, “Barry Goldwater’s Hard Line” (editorial), pg. 8, col. 2:
That seems likely to be the key issue of the 1960 campaign—the hard liners of both parties vs. the moderationists of both parties—the extremists lined up against the middle-of-the-roaders—the men of action vs. the men of reason—the punch-it-outers vs. the talk-it-outers.
 
Google News Archive
21 October 1960, Windsor (Ontario) Star, pg. 1, col. 4:
U.S. Adopts
“Hard Line”
Against Cuba
WASHINGTON (UPI)—The United States put its relationship with Cuba on a new, hard footing today, recalling its ambassador from Havana for “extended consultations.”
 
Google News Archive
12 December 1960, Meriden (CT) Record, “Kremlin Line May Not Be Same As World Communist Policies” by Preston Grover, pg. 6, cols. 5-6:
Both take a hard line challenging the United States and an almost equally hard line against West Germany.
 
Google News Archive
30 November 1961, Meriden (CT) Record, “Kennedy Looks To Tradition In Government” by William S. White, pg. 6, col. 3:
DESPITE NOTIONS to the contrary, Prof. Rostow, who now becomes head of the Policy Planning Board at the State Department, is essentially a hard-liner in all dealings with international communism.
(...)
Indeed, the hard-liners—including the newly appointed Averell Harriman and the newly promoted George McGhee of Texas—now hold every vital post in the State Department.
 
Google News Archive
17 February 1962, Mount Airy (NC) News, “Here’s For Belt-Tightening” (editorial), pg. 4A, col. 1:
On the one hand, Detroit auto makers—armed with powerful union clout—have long been hard-liners on salaries and benefits.