It's not just allowed it's required that's why northerner spends the money on the stickers attached to the cans. If you look at the bottom of a can from sweden it's says roughly this tobacco product is addictive and may negatively impact your health which seems an appropriate label in the right place too so it doesn't mess up the design.
There were a lot of epidemiological studies in sweden, one involving 120,000 construction workers showing swedish snus isn't associated with mouth cancer or any others really, the study was by I believe the swedish government,they found a weak association with pancreatic cancer (I think it was 8.1 out of 100,000 vs. 3.9 out of 100,000 for non-smokers. Sweden has one the lowest rate of pancreatic cancer in europe though I think americans have a higher risk. It was also 13 out of 100,000 for smokers), they found no increase in cardiovascular disease.
The same is mostly true in the U.S. actually moist snuff increases your risk of oral cancer risk by a factor of 1-1.3 for dip, a little more for chewing tobacco, and then 4.1-13 for dry snuff (this is crushed up powder tobacco), the dry snuff study was done on 100 women in the south who had used it for 50+ years, this means your chance of dying is like 15 in 100,000, which is about the same risk as driving a car. They also said gum cancer risk is 50 times higher which could be true but the disease is extremely rare so a 50 time increase from a risk of .00001 percent is still a 99 percent chance you won't get it. They took the results from that and a couple of other studies (which usually had methodical problems not controlling for alcohol consumption, or in a lot of cases smoking etc.) made a law all smokeless tobacco containers must contain the warnings this product may cause mouth cancer, this product is not a safe alternative to smoking, and this product may cause gum disease and tooth lose in 1984. or so and then banned TV advertising and started an anti smokeless tobacco campaign.
My opinion is that either most politicians don't know the relative risk of snus and other smokeless tobacco or they think that all tobacco should be banned. The risk could be higher I doubt it's "healthy" but neither is anything really. Some of them do and bring it up in congress but you haven't heard much of that in the news have you. Of course any research showing the relative risk of smokeless tobacco or e-cigarettes or any statements on it are usually slammed as the person being in the pay of big tobacco. In some cases that's true how are you going to pay for a health study on smokeless tobacco, who would want to fund it an anti tobacco group or a smokeless tobacco company. Occasionally some studies are funded and the results are smokeless tobacco not a safe alternative to smoking, but then the actual results are different.