They are upset over reforms that mean they will have to work longer to qualify for unemployment benefits.
Protests took place at ski resorts across France on Saturday as half-term heralded the start of the busy winter season.
Unions say unemployment system reforms, set to be implemented on April 1, will reduce benefits for seasonal workers. They will have to work six months in a two-year period to qualify for unemployment payouts, against four months in the last 28 at present.
The actions saw some ski resorts partially closed. Protesters distributed flyers or chanted by ski chairlifts.
In total there were around 50 protests organised by trade unions CGT and FO across France, from the Alps to the Pyrenees.
In Moûtiers, in the Savoie region, or in Deux-Alpes in Isère near Lyon, at least 200 seasonal workers took part in protests.
In Hautes-Pyrénées, protesters planned to rally in front of the regional prefecture to drop off their skis and shoes by the building's entrance.
"Precarity will rise with these reforms", Christine Dupuis, who works at La Plagne as a seasonal worker during winter and summer seasons, told AFP. "We will need six months, instead of four currently, to ask for our allowance."
The problem for seasonal workers is that six-months-long seasons don't exist, Maud Goret, seasonal worker and CGT representative in Font-Romeu-Pyrénées, explained to AFP. "And the winter season is getting shorter by the year."
In Goret's ski station, half of the staff is on strike.
In France's Massif central, seasonal workers have chosen to hold protests that will be visible without reducing access to ski stations - especially as some are already closed due to a lack of snow.
In Lioran, Cantal, only 13 out of 14 stations are open this February.
"We are wearing signs that read 'Seasonal workers going extinct'", Stéphanie Tantot said. She sells day tickets in a ski station and fears that her allowance may be cut in half.
The reform is aimed at ending a system in which people working on and off, on short contracts like those of seasonal workers, get the same unemployment allowance as people working on longer, more secure contracts.
"The risk is a penury of work contracts, and we know what economic impact that would have on ski stations," Fabrice Michaud, secretary-general at the CGT's transport section, told the AFP.
Blandine Vernardet, director of the Grand Tourmalet station, one of the French Pyrenees' biggest, confirmed that the work of seasonal workers is essential for the sector.
"The seasonal worker status is directly linked to our activity, we can't function without them," she said.
Two-thirds of her station's staff were absent on Saturday, leading to only 40% of the station being open that day, compared to 85% the rest of the week.
In Moûtiers, in the Alps, 200 protesters partly blocked traffic on Saturday morning then went to meet tourists who arrived at the train station.
"Welcome tourists and long live the seasonal workers!" a man working as a ski patroller
The French Labour ministry is expected to introduce an "assistance plan" for seasonal workers in ski stations next week, as it has acknowledged that mountain sports sectors such as theirs are industries with "simply no jobs in spring and autumn in some valleys".
According to the ministry's statistics office, over a million people were on a seasonal contract (of an average of two months) between April 2018 and March 2019.
Over half of French seasonal workers are in the restaurant, housing or leisure sectors, mostly on holiday resorts.