The plight of workers provides one of the most interesting examples of how theory and reality could be at odds in the Soviet Union. I'm not in a position to make international comparisons but let me give you a very quick run-down of how workers' rights were applied in practice in the early USSR.

From the outset Soviet Russia explicitly cast itself as a workers (and peasants') state, the apogee of a revolutionary working class movement. Unsurprisingly one result of the October Revolution was a greatly revised labour code. This provided for an eight hour day, strong safeguards against dismissal, the right to strike, worker input into pay/discipline/etc discussions with management, etc. Importantly, it also provided for greatly strengthened union presence in enterprises, through which the above were to be provided. As with civil law codes, this was far in advance of most contemporary nations.

(I'm going to skip over the question of workers' control over industry for the sake of brevity. That's a whole new question.)

But how the Russian proletariat was to interact with the world's first proletarian state was a question that occupied a great deal of intellectual energy during the years of civil war. In particular, what role were the unions to play in relation to the state? Tensions within the Bolshevik Party on this topic exploded into the 'trade union controversy' of 1921: the Workers Opposition demanded that management of industry be placed in union hands (because who better to build socialism than bona fide workers?), while Trotsky argued for the militarisation of industry via labour armies (because how can the proletarian state act against workers' interests?). Lenin's compromise position (leaving the unions with their autonomy) won the day but the basic question of union/state relations remained largely unresolved.

This was important because going into the 1920s the unions were central to Soviet working life. At a factory level they were heavily involved in day-to-day affairs, under the principle of triangle (treugol'nik) management: enterprises were run by the director, unions and the party cell. They negotiated wage scales, reviewed/signed-off dismissals, managed factory housing/amenities, ran cultural activities and generally represented the workers in conflicts with management. The latter included taking grievances to the national Rates and Disputes Commissions (RKK), which in the mid-1920s generally ruled favourably towards the workers. This translated into political authority: union organisers formed a formidable faction of the Party, with their head, Mikhail Tomsky, an important Politburo player.

So in the 1920s Soviet workers possessed a range of workplace rights, considerably in advance of Western nations at the time. But, as with all rights, these were only as solid as the institutions that guaranteed them. The turn towards faster industrialisation in the late 1920s saw the role of unions challenged once again. Implicitly revising the criticisms of the 1921 crisis, the hyper-industrialisers (ie Stalin's faction) once again questioned the autonomy of the unions. Everything, so the argument went, should be bent towards growing Soviet industry and strengthening the proletarian state. Unions and other such institutions were therefore instructed to 'face towards production', prioritising economic targets over representing workers in disputes ('tailism'). Tomsky was dismissed in 1929 and from here on the unions effectively become an arm of the state.

The resulting industrialisation drive was brutal for most workers. Alec Nove (Economic History of the USSR) called it "the most precipitous peacetime decline in living standards known in recorded history"; shortages were severe, real wages fell and millions of new workers endured the most basic of amenities on remote sites. Legal rights were correspondingly curtailed - abolition of striking, additional shifts and night work, forced loans, labour passports, piece rates, truancy charges, etc.

Yet the Soviet state was not all-powerful at the level of the factory floor. The chaos of the Soviet economy created its own opportunities. This can be seen in legislation: despite draconian labour laws in the late 1930s (which, amongst other features, made being late for work a criminal offence), turnover and absenteeism remained high, requiring repeated legislation to tackle the problem. Similarly, strictures on moving jobs were largely ignored and wage rates fixed to favour workers. New laws could only achieve so much.

Given the high labour turnover and pressures to meet plan targets, enterprise managers and foremen had more incentives than ever to look the other way at such 'labour offences'. Workers and managers had a shared interest in subverting the state's plans. Their unions may have been de-fanged and their rights sharply curtailed but workers were still able to negotiate the Soviet system and maintain some level of control over the production process.

Much of Stalin's labour legislation fell by the wayside after his death; I can't speak to that in detail. But the basic institutions (eg unions) and practices (of subverting the state's plans) remained until the end. Its representative unions would never be as strong as in the 1920s and its rights would never live up to the promise of 1917 but the vagaries of the Soviet system still allowed workers to retain considerable power on the factory floor.

Reading

A lot of this, particularly around institutions, is best illustrated via case study. I'm a fan of Kevin Murphy's Revolution and Counterrevolution, which looks at one Moscow factory post-revolution. Much of the thesis on subversion of Stalinist labour laws was originally proposed by Donald Filtzer, see in particular his Soviet Workers and Stalinist Industrialisation.

/u/International_KB gave a great answer that I won't try to compete with, but I'd like to say that if you're interested in the life of a Soviet worker under Stalin, Behind the Urals by John Scott is one of the most interesting books I've read in a long time. John Scott was an American who moved to the USSR in the 1930s to work as a welder to build a city behind the Ural mountains and describes in great detail what the lives of the workers around him were like. According to Scott, working conditions were brutal and there were many accidents, but he attributes those mostly to the fact that he's working in a remote area of the Soviet Union without access to a lot of basic services and supplies, and the fact that a lot of the workers were young and/or came from the peasant communes.

I'm on my phone as I type this and as such can't go into detail, but I can wholeheartedly recommend Al Szymanski's Human Rights in the Soviet Union on this question; written in the 80s, it examines the day-to-day economic and social life of Soviet citizens, and it has extensive info regarding the rights and privileges of workers in the Soviet economy. Despite what the name may lead you to believe, it is a pro-Soviet work, so keep in mind its biases; however, it is unique in that it uses sources written mostly by western analysts to make its point.