Also known as ‘Forest Brothers’, these guerrillas caused trouble in the L.S.S.R. since the 1940s and did not surrender until 1956, when the few remaining realised the futility of their resistance. Of note is that many of them were former Axis collaborators, which even antisocialist sources can confirm. For example:

‘The [Axis], in cooperation with the Forest Brothers, took Narva on August 17 and Tallinn on August 28, 1941. […] When the [Axis] withdrew from the Baltic states in 1944 (Section 1.9.2), they allowed Estonian and Latvians who had been inducted into the German Army to stay in their native countries in order to harass the Soviet Army by means of Guerrilla attacks.)’

(Source.)

Another example:

‘The organization of the partisan movement started in Latgalia on the winter 1944-1945. In Courland after the end of the war partisans were mostly former Waffen SS Legion members vanished in forests and formed partisan ranks. North Courland Partisan Organization, Latvian National Partisan Organization, “The Hawks of the Fatherland” were part of the Courlad combat movements.’

You needn’t judge them based on their Axis collaboration alone, though. The author continues:

‘On May 25 1945 partisans burned down the Bērzpils executive committee. The Tilža parish center was assaulted in the night burning down the executive building. In Jersika partisans raided the parish executive building killing major Parfenov and captured two Soviet food trucks. In retreat partisans blew up the bridge. Many villages were taken, Soviet activists were constantly under threat and shops were raided. In case of shops, milking farms and money transports partisans spared peoples life’s. [sic] But when they encountered soviet activists- the party organizers, committee workers and executive chiefs they were usually executed. […] Partisans started attacks on the soviet activists killing all their families. In Jēkabpils parish partisans ambushed and eliminated whole MGB command. Since the collectivization was underway partisans now attacked the local kolkhoz chiefs.’

(Source. The author admits that they ‘became more viscous and murdered the whole families of soviet officials and fighters’ but tries to balance that with the vague claim that the ‘NKVD was no less brutal to partisan woman and children.’ Whether or not that would justify the anticommunists’ familicides I leave that up to you.)

Lastly, it’s worth mentioning that some of these anticommunists had links to the British ruling class. Quoting Ben Wheatley’s British Intelligence and Hitler's Empire in the Soviet Union, 1941-1945, page 42:

‘SIS recruited several agents who had been former members of the Baltic SS, for it was believed that their knowledge of the Red Army could prove invaluable against a hostile Soviet Union in the post‐war era. Some of these agents would be sent back to Latvia in 1946 by speedboat in order to establish contact with the continuing 'Forest Brothers' resistance movement, which was largely made up of former Baltic SS members who had not been so fortunate as to be transferred west towards the end of the war.’